Is there a shekel's worth a difference for Israel between Mahmoud Ahmadinejad and Mir Hossein Mousavi? Yes, but the crisis is not between them but concerns the nature of the regime, future policies and the viability of the Iranian opposition to facilitate internal regime change. Foreign Minister Avigdor Lieberman pointed to a consensus among Iranian presidential candidates - commitment to nuclear capability and hatred of Israel. The Lieberman view is increasingly out of date because of events on the ground. Mossad chief Meir Dagan told the Knesset that Mousavi always supported the Iranian nuclear program, but Dagan's view is being overtaken by events on the streets of Iran's cities. On the basis of research of the Iran Policy Committee, (IPC), the nature of the regime in Teheran mattered more than personalities occupying the presidency. So long as the "rule of the jurisprudent" principle was intact, Supreme Leader Ayatollah Ali Khamenei would have final say, but the nature of the regime is changing under the weight of politics of the street. Demonstrations weaken Khamenei's legitimacy; although Mousavi has not questioned that authority (yet) and is also a child of the revolution, he is being swept up by an opposition movement and redefined by it and regime repression. IDEOLOGY HAS been the driving force in Teheran's decision regarding Israel under Ayatollahs Khomeini and Khamenei. This conclusion derives from a systematic analysis of Iranian regime statements about Israel from 1979 through 2005. By analyzing perception of threat and expression of hostility statements, IPC researchers inferred how Iran's attitude evolved over time. Perception of threat is the degree Iranian elites perceive danger; expression of hostility is the relative judgment they make about Israel. When the nature of the regime was dominant over personalities of politicians, it did not matter who was president. In this respect, the IPC study showed that Iran perceived little threat from Israel but nevertheless projected substantial hostility toward it: Israel stood as Iran's ideological foe in the Middle East. But post-2009 Iranian elections allow for a greater play of personality in a way that could mean less hostility toward Israel based on ideology. And because the US remains in Iraq, bogged down in Afghanistan and engaged in covert war against the Taliban in Pakistan, the Iranian regime under a strong Khamenei discounted the credibility of US military threats. But with challenges to the regime by an opposition movement over which Mousavi rides but has little control, Washington can exercise new leverage on Teheran. A weaker Khamenei is more likely to make diplomatic concessions. BECAUSE THE regime of Khamenei and Ahmadinejad was so hostile toward Israel, the movement for democracy opens the door to the possibility that a democratic Iran would be less of a threat to the neighborhood, including Israel. Just as there was consensus among Khamenei, Ahmadinejad and Mousavi regarding Israel, they were in accord on perceptions of the main Iranian opposition group, the National Council of Resistance of Iran (NCRI) and its largest unit, the Mujahedeen-e Khalq (MeK). Indeed, during the election campaign, the two major candidates competed as to whether they would be tougher on the MeK. And Khamenei made elimination of the MeK based in neighboring Iraq with an extensive network within Iran, a top priority for Teheran in its relations with Baghdad. Street politics in Iran include many Iranians with ties to the MeK. Many of its supporters met on June 20, 2009 outside Paris; the event included tens of thousands of Europeans and Iranian expatriates. The rally occurred on the eighth day of the national uprising of Iranians. Because these two largest opposition organizations are involved in the unrest, they are in a position to place internal regime change on the table. Regime change from within requires an organized opposition not simply a movement based on the whims of the crowd. With the organizational skills of the MeK, as indicated by the massive turnout of a worldwide gathering of supporters, this dissident organization provides heft to the pro-democracy movement. And because the Iranian system lacks the kind of political parties present in democratic countries, the movement in Iran needs the MeK. The Iranian regime's antipathy toward the MeK is not only because this organization has potential for threatening the regime; the MeK as a member of the NCRI - a coalition of religious and secular groups - is also an ideological challenge to the regime in the same manner that Israel is threat. Iranian clerics saw themselves locked in an ideological battle against encroaching forces of modernization, secularization and democratization. Because Israel also personified these factors, it was bound to come in conflict with an Islamist Iran. Research of the IPC finds that the NCRI positions itself as a modern, secular, democratic force that allows for religious diversity among its adherents, which Israel also represents; thus, the NCRI is an ideological threat to the regime of Khamenei. His "rule of the jurisprudent," permitting him to reign, has no place in the NCRI; hence, the Iranian regime has no place for the NCRI. As a proponent of modernization, secularization and democratization, the opposition movement should be less of a threat to Israel than the current regime. Now is the time for Israel and its supporters to focus on the Iranian opposition to complement economic sanctions and as an alternative to the regime that has been a growing threat to Israel. The writer is president of the Iran Policy Committee; he was a member of the National Security Council staff and personal representative of the secretary of defense in the Reagan-Bush administration. He taught six times at the Hebrew University of Jerusalem. His latest book is President Obama and Iraq: Toward a Responsible Troop Drawdown.