In the end, so it seems, it wasn’t so serious. Prime Minister Ariel Sharon had a mild stroke, was rushed to the hospital, quickly recovered full consciousness and motor control, and within hours assured a worried Israel that he was all right and would soon be back on the job. And yet to think of what might have happened had it been worse is to be given a sobering reminder of the risks Mr. Sharon took, not only for himself, but for the nation, when he bolted the Likud last month to found, several months before national elections, a new party of his own called Kadima.

Imagine a future like the following:

December 18. Prime Minister Ariel Sharon is rushed to the hospital. After a day of medical tests, conflicting rumors, and public confusion, the doctors announce that he has suffered a moderate stroke. Although there is no immediate danger to his life, his speech and motor functions have been partially impaired.

December 18-January 1. Minister of Finance Ehud Olmert, Mr. Sharon’s official second-in-command, becomes acting prime minister. Mr. Olmert, a veteran but uncharismatic politician who left the Likud with Mr. Sharon and has little popular support, seeks to postpone the early national elections, scheduled for March 28 on Mr. Sharon’s initiative. Frantic maneuverings take place in the Knesset. Opposed by Labor Party head Amir Peretz, who hopes to take advantage of Mr. Sharon’s condition to win the March 28 vote, Mr. Olmert’s move fails.

January 1-January 15. Kadima debates what to do. Not only does Mr. Sharon have no obvious heir, the new party has no recognized institutions or formal procedures for choosing one. Ehud Olmert claims the right to be its leader; others, such as Justice Minister Tsipi Livni, Transportation Minister Meir Shitreet, and Defense Minister Shaul Mofaz, all leading ex-Likudniks themselves, oppose him and propose themselves in his place. Other Kadima members suggest sticking with Mr. Sharon, whose condition has improved but whose speech is still slurred and whose appearance is worrisome. However, a brief television appearance arranged for him in the hope of convincing the public that he can function politically turns into a fiasco when he forgets the name of his own party.

January 15-30. Kadima, still leaderless, plunges in the polls. Olmert, Livni, Shitreet, and other high Kadima figures agree on party primaries – but since Kadima has no registered rank-and-file members, this can only be done by opening the vote to the general public and allowing all candidates to run.

February 10. Kadima primaries are held with 19 candidates on the ballot. Both Labor and the Likud encourage their own voters to take part in them. The winner by a narrow margin, elected by ballots of Labor Party crossovers, is Shimon Peres.

February 11-February 28. Kadima begins to fall apart. Ex-Likud ministers Olmert, Livni, Shitreet, and Mofaz refuse to accept Mr. Peres’s leadership and resign from the party. Many others leave as well.

March 1-March 28. Shimon Peres decides to run anyway. Although many Kadima supporters decide to return to the fold of the Likud, or to vote for other parties, many Labor voters, disenchanted with Amir Peretz, switch to Mr. Peres. Ariel Sharon, now in retirement on his ranch in the Negev, refuses to endorse any anyone.

March 28. Elections are held. Voter turnout, held down by cynicism and apathy in the wake of developments, is the lowest in Israel’s history. Labor, Kadima, and Likud each win about 20 votes in the 120-member Knesset. Even after long and laborious coalition negotiations, none of the three is able to form a coalition. New elections are announced for June. Meanwhile Ehud Olmert will continue to govern without a party or public to support him. Mr. Peres announces that he will not run again. Kadima finishes falling apart. The political map reverts to what it was before Ariel Sharon founded Kadima, with Labor and the Likud as the country’s two major parties and numerous splinter groups on either side of them. Yet Israel has been through six months of political chaos and it is not clear that the end is in sight.

This is of course a fanciful scenario. Starting with Ariel Sharon’s having to drop out of politics for reasons of health, one could easily write other scenarios as well. Some might end better, some worse.

And yet all would point to the same conclusion. At the age of 78, a political leader who so precipitously sets out to refashion the political system of his country that he himself remains its sole point of stability is doing something that is potentially very dangerous. Mr. Sharon’s Kadima is not a real political party. It has no members apart from its candidates for the Knesset, no national structure, no local chapters, no regulations or by-laws, no way of making decisions. Without Ariel Sharon, it is nothing and would not last long.

Nor is it just a question of getting through the period between now and the elections. Even if Mr. Sharon stays healthy and wins them and continues to serve as Israel’s prime minister, anything happening to him in the years ahead could send Israeli politics spinning out of control.

A month ago, when Mr. Sharon announced that he was leaving the Likud to found a new party, I wrote a column in this newspaper questioning how wise it was of him to do so. This was not because I did not agree with his policies, but because I did, and because these policies should not be allowed to depend on the health of a single man. They need a political organization to give them durability and continuity. At the very least Mr. Sharon had better make it his business to turn Kadima into such an organization in a hurry, and to lay down rules for how it should pick his successor.

Mr. Halkin is a contributing editor of The New York Sun.