The stroke suffered by Prime Minister Ariel Sharon could prove to be one of the great disasters in the country's near-60-year history. As I write this, Sharon's condition remains uncertain, but the severity of his stroke makes it unlikely that he will return to power. That could be disastrous because Sharon represented, indeed embodied, the emergence of a rational, farsighted national idea that seemed poised in the coming elections to create a stable governing political center for the first time in decades. For a generation, Israeli politics have offered two alternatives. The Left said: We have to negotiate peace with the Palestinians. The Right said: There's no one to talk to because they don't want to make peace; they want to destroy us, so we stay in the occupied territories and try to integrate them into Israel. The Left was given its chance with the 1993 Oslo peace accords. They proved a fraud and a deception. The PLO used Israeli concessions to create an armed and militant Palestinian terror apparatus right in the heart of the West Bank and Gaza Strip. Israel's offer of an extremely generous peace at Camp David in the summer of 2000 was met with a savage terror campaign, the second intifada, that killed a thousand Jews. (Given Israel's tiny size, the American equivalent would be 50,000 dead.) With the Left then discredited, Israel turned to the Right, electing Sharon in 2001. But the Right's idea of hanging onto the territories indefinitely was untenable. Ruling a young, radicalized, growing Arab population committed to Palestinian independence was not only too costly but ultimately futile. SHARON'S GENIUS was to seize upon and begin implementing a third way. With a negotiated peace illusory and a Greater Israel untenable, he argued that the only way to security was a unilateral redrawing of Israel's boundaries by building a fence around a new Israel and withdrawing Israeli soldiers and settlers from the other side. The other side would become independent Palestine. Accordingly, Sharon withdrew Israel entirely from Gaza. On the other front, the West Bank, the separation fence now under construction will give the new Palestine about 93 percent of the West Bank. Israel's 7 percent share will encompass a sizable majority of Israelis who live on the West Bank. The rest, everyone understands, will have to evacuate back to Israel. The success of this fence-plus-unilateral-withdrawal strategy is easily seen in the collapse of the intifada. Palestinian terror attacks are down 90 percent. Israel's economy has revived. In 2005 it grew at the fastest rate in the entire West. Tourists are back and the country has regained its confidence. The Sharon idea of a smaller but secure and demographically Jewish Israel garnered broad public support, marginalized the old parties of the Left and Right, and was on the verge of electoral success that would establish a new political center to carry on this strategy. The problem is that the vehicle for this Sharonist centrism, his new Kadima Party, is only a few weeks old, has no institutional structure, and is hugely dependent on the charisma of and public trust in Sharon. To be sure, Kadima is not a one-man party. It immediately drew large numbers of defectors from the old Left and Right parties (Labor and Likud), including Cabinet members and members of parliament. It will not collapse overnight. But Sharon's passing from the scene will weaken it in the coming March elections and will jeopardize its future. Sharon needed time, perhaps just a year or two, to rule the country as Kadima leader, lay down its institutional roots and groom a new generation of party leaders to take over after him. This will not now happen. There is no one in the country, let alone in his party, with his prestige and standing. Acting Prime Minister Ehud Olmert, his deputy, is far less likely to score the kind of electoral victory that would allow a stable governing majority. Kadima represents an idea whose time has come. But not all ideas whose time has come realize themselves. They need real historical actors to carry them through. Sharon was a historical actor of enormous proportion, having served in every one of Israel's wars from its founding in 1948, having almost single-handedly saved Israel with his daring crossing of the Suez Canal in the 1973 Yom Kippur War, and now having broken Israel's left-right political duopoly that had left the country bereft of any strategic ideas to navigate the post-Oslo world. Sharon put Israel on the only rational strategic path out of that wreckage. But, alas, he had taken his country only halfway there when he himself was taken away. And he left no Joshua. The writer is a columnist for The Washington Post.