As George W. Bush prepares to leave town, one of the many pieces of unfinished business is his vow to thwart Iran's nuclear ambitions. Instead, Teheran is far closer today to having a nuclear weapon than when he came to office. His refusal to engage in any substantive dialogue with the Iranians unless they first accepted his terms may explain why all three presidential contenders have promised greater emphasis on diplomacy. Democrats Barack Obama and Hillary Clinton have been particularly emphatic about that - Obama even offering unconditional talks with Iranian President Mahmoud Ahmadinejad - and Republican John McCain has called for stepped-up diplomatic and economic pressure. McCain has said public support for military action would be difficult because Bush's invasion of Iraq, which he said was based on faulty intelligence, squandered American credibility. It would take a "clear and present danger" to the United States to justify military force against Iran, he has said. When asked in their Philadelphia debate last week how they would respond to an Iranian nuclear attack on Israel, Obama said he would take "appropriate action," while Sen. Hillary Clinton vowed "massive retaliation." Iran seemed to get a reprieve in December when the National Intelligence Estimate concluded it had shelved its nuclear weapons program in 2003, but that headline-grabber overshadowed the finding that "Iran has the scientific, technical and industrial capacity eventually to produce nuclear weapons if it decides to do so." Israeli officials were alarmed that much of the international community would read only the first line and feel they'd just been let off the hook. Where Israeli and American leaders see a looming threat, the Russians, Chinese and Europeans see economic opportunity. Israel's great worry is that if most other countries don't take the Iranian threat seriously enough, they may be compelled to act on their own. And that has to scare the ayatollahs, especially if they think those Zionists really are crazy and unpredictable. IRAN'S DANGER is more than a nuclear weapon that may be years away. It is its financing, training, weapons and diplomatic cover for a terror network that targets Israel. Teheran is also spreading its influence across the Middle East - with a U.S.-provided foothold in previous enemy Iraq - that threatens not only Israel but also American's traditional friends in the Arab world. A nuclear weapon will be a potent instrument of blackmail for Iran and an umbrella for its terrorist allies. The threat to Israel should not be underestimated, but Iran has much more reason to worry. Iran's nuclear weapon is still theoretical; Israel's is not. Israel is widely believed to have several hundred nuclear warheads, and its delivery systems are far more advanced, accurate and diverse than Iran's. Iran is developing ballistic missiles, with North Korean help, and they are believed capable of hitting Israel. Israeli long range Jericho missiles are accurate and reliable. Iran has nothing to match Israel's batteries of the Arrow anti-missile missiles. Iran's air force is barely functional; Israel's is one of the best in the world. Israel's German-built Dolphin submarines, according to some reports, may be equipped with nuclear-tipped cruise missiles, giving Israel a nuclear triad: airplanes, missiles and submarines. That gives Israel a powerful deterrent: a second strike capability, a Cold War concept indicating the ability to launch nuclear missiles even after a country has absorbed a heavy first blow. Israeli military officials have said they don't have the number of planes, missiles, aerial tankers and other systems needed to go after all of Iran's nuclear installations - which are widely scattered and deeply buried - even if they knew where to find them. But they do have the capacity to wreak enormous damage on the country's energy infrastructure and other assets. THE AYATOLLAHS are perfectly willing to send thousands of children to die in a war with Iraq or suicide bombers to Israel, but you won't see any of them strapping on explosive belts themselves. They are not suicidal; their goal is not to die for the Islamic republic but to let others do the dying while they spread the Shiite revolution to the Sunni Arabs. They know that a nuclear attack on Israel will bring the kind massive retaliation that will leave their revolution in cinders. For Israel, war against a nation state like Iran means no targets are off limits - unlike going after terror groups hiding among the civilian population in Lebanon or Gaza. Israel would have no compunction about visiting shock and awe on Iran, unfettered by delusions of converting it to democracy. Iranian leaders seem to compete with each other in threatening to obliterate Israel, but when Israelis respond with their own bravado, the Iranians run crying to the UN, filing formal protests. Every recent Israeli prime minister has considered Iran the one enemy which can pose an existential threat, and they have focused much of their diplomacy on trying to get the international community to take Iranian nuclear ambitions seriously as a global threat and not just as an Israeli problem. The next American president clearly understands that, but also that the Bush administration's "no diplomacy" policy only made a bad situation worse. And polls show the American Jewish community feels the same way.