As I write these lines, early on Thursday morning in Israel, Ariel Sharon is in an operating room in Jerusalem’s Hadassah Hospital, undergoing brain surgery. His situation appears to be extremely serious. So does the country’s.

Two things seem definite. One is that, whether or not Mr. Sharon pulls through, and whatever his rate of physical and mental recovery, he will not be able to lead his new Kadima Party in the election campaign now getting under way. The other is that everything that has been predicted about this campaign, about the government that will emerge from it, and about this government’s policies can now be tossed out the window. As of this moment, Israel is in a state of political uncertainty such as it has never known in its 58-year-old history.

To say that Kadima, which every poll showed winning the March elections by a large margin, was until tonight a one-man party is not entirely accurate. It was indeed run by one man, on whose great popularity its fortunes rested, but it was not yet a true party at all and it had none of the institutions or by-laws of one. Without Mr. Sharon it is little more than a roster of prominent politicians and public figures who could be fitted into a large living room.

Kadima’s de facto head in Mr. Sharon’s absence is, but only tenuously, Acting Prime Minister Ehud Olmert, a veteran Likud politician who has been close to Mr. Sharon for years and was among the advisers who most encouraged him to bolt the Likud. As Mr. Sharon’s deputy prime minister, Mr. Olmert has automatically assumed the country’s leadership now that Mr. Sharon is incapacitated. Had Mr. Sharon’s latest stroke taken place a few days from now, after the choosing of Kadima’s Knesset list, on which Mr. Olmert was expected to be Number Two, the latter would have been recognized by his fellow Kadima politicians as the party’s new leader, too.

But Mr. Sharon had his stroke tonight, and since Kadima’s Knesset list was slated to be handpicked by him without any formal proceedings, there are now no rules for choosing it. It’s not even possible to say, “Let those in the living room decide,” because there is no official guest list and no way of determining who is invited and who would be crashing the party.

Were he a popular or charismatic figure in his own right, his position as Mr. Sharon’s temporary replacement would have enabled Mr. Olmert to seize Kadima’s reins by means of an informal consensus of his peers. Yet, a capable but lusterless politician, he is neither of those things. There are others in the new party, such as Shimon Peres and former Likud minister of justice Tsipi Livni, who may feel they are better suited to head it and lead it to an electoral victory. Yet whom are they supposed to convince of this and how?

It is not impossible that Kadima will simply disintegrate in a fit of squabbling, vanishing as quickly as it was formed. In that case, there are two possibilities. One is that the elections, which were advanced from November to March on Mr. Sharon’s initiative, would be held anyway, with Labor and Likud now vying to win them rather than to be Kadima’s runner-up. The other is that the same Knesset that voted to advance them would now vote to move them back again.

According to law, Mr. Olmert would then serve as acting prime minister for one hundred days, that is, until early April, after which the Knesset would be asked to choose another prime minister to serve until November. Yet so badly would the Knesset be split, now that its largest party, the Likud, has only 27 out of 120 seats after the Sharonites’ defection from it, that it might not be able to choose anyone, forcing elections to be moved up again.

A more likely scenario is that Kadima, even though some of its politicians might seek to return to the parties they deserted for it, will find some way of cobbling together a Knesset list and that the elections will be held on schedule. Yet no matter who headed it and was on it, such a list would win nowhere near the 40+ seats predicted by the polls for it under Ariel Sharon. It would rather be a semi-cadaver picked apart by the same parties – mainly Labor, Likud, and the centrist Shinui – on which it had fattened until now. The result of this would be, once again, a fractured Knesset in which even the largest party – almost certainly Labor or Likud – would enjoy a far from commanding position. Coalition negotiations would be long and tortuous, and the government formed by them weak and unstable.

What a turnabout from the Israel of 24 hours ago! Then the results of the March elections seemed a foregone conclusion. So did the strong, activist government under Ariel Sharon that seemed sure to emerge from them, as well as the agenda that this government would have – at the top of which would have been Ariel Sharon’s determination to ease Israel out of its conflict with the Palestinians by a withdrawal on the West Bank, modeled on the disengagement from Gaza, to the security fence now under construction.

A country on which a new mood of confidence had settled following the breaking of the Palestinian intifada and the successful Gaza disengagement, both accomplishments for which Ariel Sharon deserved full credit, is now a confused and worried one.

Mr. Sharon will go down as one of the best prime ministers in Israel’s history, one who won a war against terror that was deemed unwinnable and restored a sense of direction to a people that had lost it. Yet if, as has often been said, one mark of a great leader is his making sure that he has a successor, or that there is at least a clear procedure for choosing one, Mr. Sharon fell short of greatness. In impetuously leaving the Likud to found Kadima, it never occurred to him that, at the age of 77, he would not be around for at least a few more years. It should have, though. That’s not the kind of oversight that a meticulous planner like him should have been guilty of.

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