Barack Obama: When I traveled to Israel last year, I met with Israelis across the political spectrum and heard the diversity of views for which Israel is famous. But on one issue, there was consensus: a deep concern about the threat posed by an Iran armed with nuclear weapons. Israelis are right to be concerned. A nuclear weapon in the hands of this radical theocracy could have dire consequences: a nuclear arms race drawing in Egypt, Saudi Arabia, and Turkey; pressure on other nations to accommodate Iranian demands; emboldened terrorist groups acting under an Iranian nuclear umbrella; and, perhaps, the proliferation of nuclear technology to other states and terrorist groups. For Israelis, the threat is even more pronounced in light of Iranian President Mahmoud Ahmadinejad's denial of the Holocaust and chilling call for Israel to be "wiped from the map." Israel does not have the luxury of treating these threats as mere rhetoric. Neither should the United States. Unfortunately, recent findings by the International Atomic Energy Agency (IAEA) suggest that Iran has made considerable progress - more than had been realized - toward mastering the technology required to build nuclear weapons. So the need to address this threat is urgent. In facing such a threat, no President of the United States should take any option, including the military option, off the table. But at this stage, our first line of offense must be a sustained, aggressive, coordinated diplomatic effort to make clear to Iran the costs of its current path. The current strategy of ignoring Iran and issuing threats through intermediaries has not worked. I would engage Iran in direct, bilateral discussions - much as we negotiated with the Soviet Union throughout the Cold War. In these discussions, we should make clear to Iran that its continued pursuit of nuclear weapons will lead to greater isolation, and increased economic pressure. At the same time, we must communicate directly with the Iranian people, who are not as radical as their government, letting them know the opportunities for cooperation that exist if their government ends its current destructive policies. Our diplomatic offensive must include stronger multilateral actions as well. The UN Security Council has sanctioned Iran twice in the past year, but it is time to ratchet up the pressure. We must push Iran's trading partners in Europe and energy suppliers in the Gulf states to use additional economic leverage against Iran, and we must demand that the Russians and Chinese focus on the serious threat to their interests posed by a nuclear Iran. We need to build this pressure over the coming weeks and months, not months and years. And we can do more on our own. I am pushing Congress to pass my bill that makes it easier for state and local governments to divest their pension funds of companies that invest in Iran's energy sector, providing the revenue Iran uses to pursue nuclear weapons and sponsor terrorism. Divestment is a useful tool to bring additional economic pressure to bear on Iran. Finally, showing Iran we are serious means maintaining close diplomatic and military relationships with our allies in the region. In Israel's case, that means providing our full military assistance package and continuing our cooperation with Israel in the development of the missile defense technology that Israel needs to defend itself. Hillary Clinton: Iran poses a threat to our allies and our interests in the region and beyond, including the United States. The Iranian president has held a conference denying the Holocaust and has issued a series of bellicose statements calling for Israel to be wiped off the map. His statements are even more disturbing and urgent when viewed in the context of the regime's quest to acquire nuclear weapons. The Iranian regime also uses its influence and resources in the region to support terrorist elements. Hizbullah's attack against Israel last summer, using Iranian weapons, clearly demonstrates Iran's malevolent influence even beyond its borders. In light of this threat to our security, US policy must be clear and unequivocal: We cannot permit Iran to build or acquire nuclear weapons; no option can be taken off the table. We must continue to put pressure on Iran through economic sanctions. I recently joined Sen. Frank Lautenberg in sponsoring a measure to strengthen existing sanction provisions in the International Emergency Economic Powers Act, which prohibits American companies from conducting business with nations that sponsor terrorism. Some American companies have exploited a loophole in the law by creating foreign subsidiaries to do business with rogue nations like Iran. Our legislation would close the loophole. Among other options that should be pursued is a process of direct engagement with Iran, as recommended by many, including the Iraq Study Group. During the Cold War, we spoke to the Soviet Union while thousands of missiles were pointed at our cities. That was a smart strategy used by Republican and Democratic Presidents, which worked to the benefit of our national security, even though it was often a difficult one. I am encouraged that the Administration is now engaging in talks with Iran but hope that they will include the nuclear issue among the items that they raise with the Iranians. As we face the refusal of Iran to suspend their nuclear ambitions, we need to deliver a strong message that we will not stand by and tolerate this behavior. We should be able to deliver that message forcefully through direct talks. Rudy Giulani (Editor's note: Remarks said Tuesday during a GOP debate in New Hampshire when asked about the possibility of using tactical nuclear weapons to prevent Iran from going nuclear): Part of the premise of talking to Iran has to be that they have to know very clearly that it is unacceptable to the United States that they have nuclear power. I think it could be done with conventional weapons, but you can't rule out anything and you shouldn't take any option off the table. And during the debate the other night, the Democrats seemed to be back in the 1990s. They don't seem to have gotten beyond the Cold War. Iran is a threat, a nuclear threat, not just because they can deliver a nuclear warhead with missiles. They're a nuclear threat because they are the biggest state sponsor of terrorism and they can hand nuclear materials to terrorists. And we just saw it just last week in New York, an attempt by Islamic terrorists to attack JFK airport; three weeks ago, an attempt to attack Fort Dix. These are real problems. This war is not a bumper sticker. This war is a real war. Joe Biden: Iran with the bomb could spark an arms race in the Middle East, with Saudi Arabia, Egypt, and Syria joining in. Given the fault lines - between Sunni and Shia, Israelis and Palestinians, Persians and Arabs, Turks and Kurds, fundamentalists and moderates - that's the last thing we need. And it's the last thing Israel needs. No President should take any option off the table, including force. But we have time: Iran is years away from having a bomb and a missile to deliver it. We need to use the time wisely. We have to keep our eyes on the prize: preventing Iran from getting the bomb. This administration spent five years obsessed with the idea of getting rid of the Iranian regime. None of us like the regime, but think about the logic: We want you to renounce the bomb - and by the way, when you do we're still going to try to take you down. The result: Iran accelerated its efforts to get the bomb and it is much closer now than it was when President Bush took office. We need a policy that isolates Iran, not America and tips the balance in Iran against pursuing nuclear weapons. That means keeping our allies, Russia and China on the same page as we ratchet up economic and diplomatic pressure on the government to stop pursuing nuclear weapons. At the same time, there are growing fissures within the ruling elite - we need to exploit them. Above all, we have to recognize that our biggest allies in this effort are the Iranian people. They're open to America. They don't like a regime that denies them basic political and social rights and that can't deal with corruption, unemployment and inflation. The Iranian people need to know it is their government, not the US that is choosing confrontation over cooperation. So we should tone down the rhetoric and talk. It's amazing how little faith this administration has in America's ideas and ideals. Force must be the last option because it's a bad option. First, with our forces bogged down in Iraq, our threat to use force doesn't look very credible. Second, we can set back Iran's program but not stop it. Using force would lead to retaliation by Iran, including against our troops in Iraq. It would cause the Iranian people to rally behind Ahmadinejad and the extremists. Third, even a "limited" strike would be perceived as something much bigger by the Iranians and could spark a real war. The only thing worse than a poorly planned intentional war is an unplanned unintentional war. John McCain: The world's chief state sponsor of international terrorism, Iran defines itself by hostility to Israel and the United States. It is simply tragic that millennia of proud Persian history have culminated in a government today that cannot be counted among those of the world's civilized nations. When the president of Iran calls for Israel to be wiped off of the map, or asks for a world without Zionism, or suggests that Israel's Jewish population return to Europe, or calls the Holocaust a myth, it is clear that we are dealing with an evil man and a very dangerous regime. Teheran's continued pursuit of nuclear weapons clearly poses an unacceptable risk. Protected by a nuclear arsenal, Iran would feel unconstrained to sponsor terrorist attacks against any perceived enemy. Its flouting of the Nuclear Nonproliferation Treaty would render that agreement obsolete, and could induce Turkey, Egypt, Saudi Arabia and others to reassess their defense posture. Moderate Gulf states would have to accommodate the new reality, and the world would live, indefinitely, with the possibility that Teheran might pass nuclear materials or weapons to one of its allied terrorist networks. Coupled with its ballistic missile arsenal, an Iranian nuclear capability would pose an immediate and existential threat to the State of Israel. UN Security Council action is required to impose progressively tougher political and economic sanctions. Should the Security Council continue to drag its feet, the US must lead a group of like-minded countries in imposing multilateral sanctions outside the UN framework. The opposition of Russia and China to effective sanctions on Iran - and on issues ranging from Myanmar to Darfur to North Korea - is why I proposed the creation of a league of Democracies in which Israel would be welcomed. When democracies are united in addressing threats like Iran, we cannot afford to allow autocracies to thwart action. There are many ways to increase pressure on Iran. Financial sanctions have had an initial effect. Iran's need to import refined gasoline, to cite one example, suggests an important vulnerability. And countries such as China and Malaysia, which have signed deals to develop Iranian gas fields, and Russia, which provides weapons systems to Teheran, should know that Iran would be a critical element in American's bilateral relations with each nation. In the meantime, the US should immediately investigate whether any of these deals violate the terms of last year's Iran Freedom Support Act. The US should also privatize the sanctions effort by launching a divestment campaign. By persuading individuals, pension funds, and financial institutions to divest from companies doing business with Iran, we can isolate and delegitimize a hostile government. We will also, as we did with the South Africa divestment campaign, increase the debate inside the country about whether the present course serves the interests of the Iranian people or merely those of a misguided elite. Americans and all proponents of freedom need to reassure the millions of Iranians who aspire to self-determination that we support their longing for freedom and democracy. There is much more we can and should do to translate such support into concrete action. Every option must remain on the table. Military action isn't our preference. It remains, as it always must, the last option. We have some way to go diplomatically before we need to contemplate other measures. But it is a simple observation of reality that there is only one thing worse than a military solution, and that is a nuclear-armed Iran. The regime must understand that it cannot win a showdown with the world. Mitt Romney: Iran is an intolerant, repressive regime that is developing nuclear weapons, supports terrorism and is located right near much of the world's oil and natural gas. I believe that radical Islamic jihadists and the spread of weapons of mass destruction represent the greatest threat to the world since the fall of the Soviet Union and, before that, Nazi Germany. That threat would take on an entirely new dimension if Iran were allowed to develop nuclear weapons. In January, I discussed the threat of Iran at the Herzliya Conference. Since then, Iran has done little to change its dangerous course. It has continued to operate its nuclear program in defiance of the United Nations Security Council. It has issued a new banknote that features a red nuclear symbol superimposed on the map of Iran. On April 9th, Iran marked a new national holiday - "Nuclear Day." Recently the press reported Iranian President Ahmadinejad's statement that the countdown to Israel's destruction had begun. Clearly, this is a regime that is unrelenting in its pursuit of nuclear weapons and a threat to the world To aggressively combat Iran's nuclear ambitions and exploit the regime's vulnerabilities, I have outlined a five-pronged strategy: First, we should tighten economic sanctions. Denying Iran access to the international banking system is crucial. The US and Europe should ensure that Iran finds it very difficult to obtain credit and make purchases in foreign currencies. In addition, I have called for strategic divestment among state pension funds from companies that support the Iranian regime's dangerous actions. Second, we should isolate Iran diplomatically. Of course, we keep communication channels open. Yet until there are indications that high level engagement would do anything other than reward bad behavior, America should not engage Iran in direct, bilateral negotiations over their nuclear weapons program that legitimize Iran's defiance of the world. As part of this effort, Iran's President Ahmadinejad should be indicted under the terms of the Genocide Convention for incitement to genocide. Third, Arab states must join this effort to prevent a nuclear Iran. These states should support Iraq's government; turn down the temperature of the Arab-Israeli conflict; stop the financial and weapons flows to Hamas and Hizbullah; and tell the Palestinians to drop their terror campaign and recognize Israel's right to exist. Fourth, we must make it clear to the Iranian people that while nuclear capabilities may be a source of pride, it can also be a source of peril. The military option must remain on the table. The regime should know that if nuclear material from their nation falls into the hands of terrorists and is used, it would provoke a devastating response from the civilized world. Fifth, our strategy must be integrated into a broader approach to the Muslim world. We must work with moderate Muslim communities and leaders to build a lasting Partnership for Prosperity and Progress - a global effort which would support progressive Muslim communities and leaders in every nation where radical Islam is battling modernity and moderation. This Partnership for Prosperity should help provide the tools and funding necessary for moderates to win the debate in their own societies. In the final analysis, only Muslims will be able to permanently defeat radical Islam. But we can and should support this effort. John Edwards: The situation in Iran has only gotten worse under this Administration's approach. Recently, Iran's hardliners rejected the UN's second resolution imposing new sanctions on Iran. Then, Ahmadinejad went ahead and announced his country had started enriching uranium on an industrial scale. Clearly, we need a new direction. The situation is deadly serious, but there is a path forward. We need to continue to contain Iran through measures that will force the nation, over time, to finally understand the world community will not allow it to possess nuclear weapons. You should never tie the hands of an American president or take any option off the table, but instead of focusing on military action, we should focus on the many steps in front of us that have not been used. Every major ally agrees a nuclear Iran is unacceptable, and both China and Russia recently voted with the UN Security Council to impose sanctions on Iran. We should continue to work with all these parties to help us put a system of carrots and sticks in place. We first need to be negotiating directly with Iran. Communication will give us more information and more control. At the height of the Soviet Union, we still talked with the Kremlin, and we talked with China at the height of tensions. It's good that the Administration has just begun to talk with Iran, but in many ways these short talks are too little, too late. We need a fundamental re-engagement of the country. For carrots, we should make nuclear fuel available to Iran and control the cycle, but allow Iran to use the fuel for any civilian purpose. Second, we need to offer an economic package. The Iranian economy is already struggling, and this would be very attractive to the people. And, for sticks, we need to threaten much more serious economic sanctions if Iran continues its nuclear operations. We also need to take steps to isolate Ahmadinejad, so that the moderates and those within the country who want to see Iran succeed economically, can take advantage of it. Sam Brownback: Ahmadinejad and the mullahs match genocidal rhetoric with proud defiance of international objections to their nuclear program. Their acquisition of nuclear weapons would constitute a threat to the security of the United States and the free world. This dangerous situation requires that all options remain on the table, demonstrating a credible and unwavering commitment to an Iran free of nuclear weapons. The regime should understand the consequences of intransigence. We should speak directly to Iran and make our objections to its behavior clear. We should not negotiate with the regime, however, until it stops enriching uranium and supporting terrorism. Our strong words should support strong actions. I propose a three-pronged solution to the Iranian nuclear crisis: squeeze the regime economically, undermine it politically, and expose it morally. First, economic sanctions: We can and must de-fund the regime's ability to build and sustain a nuclear program. As president, I would enforce all sanctions authorized in the Iran Sanctions Act, including against Russian, European, and Chinese corporations and financial institutions that invest in the Iranian oil and gas sectors. I would also call for additional sanctions and penalties included in the Iran Counter-Proliferation Act, of which I am a cosponsor. I also believe we should encourage individuals, corporations and other countries to divest from Iran. Second, political pressure: We must overhaul our public diplomacy efforts in Iran and challenge the regime's cynical manipulation of the nuclear issue. The Iranian people should hear that we support their desire for progress and better technology and stand with them in opposing the regime's drive for nuclear weapons. This will require US broadcasts that beam fewer hours of Britney Spears music and spend more time reporting on the regime's corruption and ineffectiveness. The Iranian people want democracy and we should give them the tools they need to reform their country from within. Third, human rights: Any regime that relies on secret police, censorship, imprisonment, and torture to maintain its grip on power ought not be trusted to maintain a "peaceful, civilian nuclear program." The Iran Human Rights Act of 2007 ( S.1534), which I introduced earlier this month, outlines ways to leverage human rights and undermine the regime's credibility inside Iran and among the community of free nations. Bill Richardson: Iran must not acquire nuclear weapons. But preventing Iran from going nuclear will require strong diplomacy backed by credible power and clarity of purpose. It also will take realism: above all, we must understand that no nation has ever been forced to renounce nukes, but that many have been persuaded to do so with a combination of carrots and sticks. We need to approach the Iranian nuclear problem with both fierce determination and with open eyes. The key is to make them see that they will be better off and more secure without nukes than with them. If we unite the world behind the right carrots and sticks, and provide the Iranians with face-saving ways to step back from the nuclear brink, we will prevail. As we know from the Cold War, deterrence is above all a matter of clarity and credibility. We need to be absolutely clear that a nuclear Iran is unacceptable, and we need to be absolutely credible when we say what we will do about it if the Iranians continue to disregard the will of the international community. The clear message must be this: develop nukes and you will face devastating global sanctions which will damage your economy and weaken you politically; desist from developing nukes and you will receive meaningful rewards, including robust security guarantees (above all from the United States), diplomatic recognition, better access to international credit and investment, guaranteed supplies of nuclear fuel from abroad, and an end to trade sanctions. This sort of engagement, with a stick in one hand and a carrot in the other, is how we got Libya to renounce nukes, and this is how we must approach Iran. For this message to be credible, the United States needs the solid support of the Europeans, China, and Russia in support of UN Security Council resolutions. If all these parties join us in sanctions, they will work. If they do not join us, they will not work. Russia is the key, because of its substantial economic interests in Iran, such as the Bushehr nuclear reactor. Preventing Iran from going nuclear is inevitably linked to the power struggle between hardliners like President Amadenejad, on the one hand, and pragmatists and moderates in the Iranian leadership, on the other. If we can keep Russia on board, the moderates and pragmatists will be strengthened. They will be further strengthened if we make sure that Iran can save face as it renounces nuclear enrichment. This is possible: Iran insists that it only wants nuclear energy, not weapons. Accordingly, a solution that guarantees them secure supplies of enriched uranium, to be monitored by the IAEA, may become politically palatable.