Exactly three years ago, Ehud Olmert first broached the idea of unilateral withdrawal from the Gaza Strip and parts of the West Bank - what was to become shortly afterwards the disengagement plan. At the time, Olmert was vice premier and trade and industry minister, filling in at the annual Ben-Gurion memorial service at Sde Boker for prime minister Ariel Sharon, who was down with the flu. Olmert was trying the waters before Sharon took the plunge. The scion of a proud revisionist family, by committing the sacrilege of agreeing to a major division of Eretz Yisrael, flew the first trial balloon for Sharon. Only when it was clear that the balloon was sailing calmly away, did Sharon publicly commit himself to the move a month later. Now Olmert is prime minister, but in his current situation he can't trust any of his ministers to launch a trial balloon for him. Neither does he feel he has the time for making too many test runs. He could barely wait 24 hours to see whether the cease-fire with the Palestinians was holding up and off he was, announcing his daring diplomatic plan, second in audacity only to Ehud Barak's offer to the Palestinians at Camp David more than six years ago. Right-wingers were quick to blame Olmert, just as they did Sharon, saying his plan was a desperate ploy to ensure his political survival by buying the support of the leftist media and legal establishment. Unlike Sharon, Olmert can point to the realignment plan he presented before the election and claim that this was already his agenda nine months ago. Still, there are two fundamental distinctions between the Olmert plan then and his Sde Boker speech on Monday. First, when Olmert was elected prime minister, he was still riding a brief wave of popularity after suddenly replacing the stricken Sharon. Today, he is leading a discredited administration that is perceived by a wide majority as having dismally failed in the Lebanon war and not done anything right since. That leads to the second difference. Before the war in Lebanon, Olmert's realignment plan was presented as a natural continuation of disengagement, a unilateral step to be taken after a token attempt to negotiate with the Palestinians. After the summer's crises in the Gaza Strip and Lebanon discredited unilateral withdrawals for the foreseeable eternity, Olmert had to adapt his plan of withdrawal into settlement blocs near the Green Line as something that could take place only as part of a joint process with the Palestinians. But why did he have to go ahead with it anyway? Olmert obviously believes that it is the only way forward. He wouldn't have been taking such political risks over the last three years if he hadn't reached the conclusion years ago that the vision of controlling the whole of Eretz Yisrael that he was brought up with was untenable. But why now? Olmert had little choice but to come out now with a major initiative, and they don't come much larger than this one. Ever since the Lebanon war ended, almost four months ago, the government has been stuck in a vicious circle of recriminations and infighting. It's not just the deep rivalry with Defense Minister Amir Peretz, it's the feeling that Kadima, only a year after its inception, is already dissolving, with opinion polls that prove Olmert isn't regaining public support. With some deft political maneuvering, Olmert has managed to deflect most of the more immediate fire over the war's mismanagement to the direction of Peretz and Chief of General Staff Lt.-Gen. Dan Halutz, who are much closer than he is to losing their jobs. Olmert also secured his flank by bringing Avigdor Lieberman into the government, thereby stabilizing his coalition. But these are short-term measures. Olmert realized he had little time to act if he wanted to ensure his continued control of Kadima, keep Labor in the coalition no matter what and start rebuilding his own shattered credibility. Hence, the need for such an ambitious plan and the haste to come out with it - the moment Kassam rockets stopped flying for a few hours. But for his plan to ever materialize, the Palestinians have to undergo some fundamental changes and developments that would throw a wrench into the spokes can't happen - like another war up north. Also, can Olmert deliver his side of the bargain? Can he sell the plan to the Israeli side? The current makeup of the Knesset actually gives him his best chance. Even if coalition partners Israel Beiteinu and Shas refuse to support him, which is quite likely, he can still get a majority in the Knesset since Meretz and the Arab MKs will have no choice but to vote in favor of such a plan. Olmert might lose a few of his own Kadima MKs - most likely settlers Othniel Schneller and Zeev Elkin. They saw themselves as go-betweens, ensuring that this government would be careful in any withdrawals. But it's hard to see how they could swallow such a total retreat. But perhaps the most difficult internal challenge for Olmert isn't in the political arena, it would be selling such an accord to the Israeli public. The traumas of disengagement from Gush Katif are still fresh in many minds. Massive civil disobedience and open mutiny in the army were only barely evaded, and that was over 8,000 settlers. Sharon's popularity and the fact that most Israelis trusted him in defense matters was a major factor in ensuring the eventual peaceful outcome. Olmert's new plan means moving, at the very least, 10 times that number of settlers. As things stand now, he has nowhere near the public stature and credibility necessary for that.