Israeli Prime Minister Ariel Sharon's stroke has left a gaping hole in the Bush administration's approach to resolving the Israeli-Palestinian conflict and stabilizing the broader Middle East.
For much of President Bush's tenure, U.S. policy in the dispute has been shaped more by Sharon's ideas than any other factor.
Sharon remained in grave condition Thursday at a hospital in Jerusalem, where he was placed in a medically induced coma after nearly eight hours of neurosurgery.
Vice Prime Minister Ehud Olmert formally assumed temporary leadership of the Israeli government, and several of Sharon's closest allies acknowledged that even if he survived the massive cerebral hemorrhage he suffered late Wednesday, it was highly unlikely he would ever be healthy enough to return to his post.
The apparent end of the Sharon era plunged Israel into a state of grief and Washington into a period of uncertainty.
The disabling of Sharon removes the most important individual driving events in this highly volatile corner of the world and the man embraced by Bush as the best chance for settling the conflict that has raged for more than half a century.
While publicly backing a step-by-step plan called the "road map" that gives each side a series of responsibilities that would lead to final settlement of the conflict, Bush in fact went along with Sharon's unilateral approach.
"Bush has a stance but not a strategy" for the Israeli-Palestinian dispute, said William Quandt, who as a senior White House advisor during the Carter administration helped negotiate the Camp David accords. "He supported Sharon."
Without Sharon, the administration faces a landscape loaded with questions and the danger of a power vacuum in Israel at a time when the Palestinian leadership is weak and ill-organized.
For Bush, Sharon's departure from the political scene comes as a personal blow. Sharon was elected prime minister just 17 days after Bush took office, making him the only Israeli leader the U.S. president has dealt with. Although Sharon could be difficult, he cultivated a personal relationship with Bush and, by most accounts, succeeded in making it work.
This set the stage for the larger political relationship between the United States and Israel.
The stakes have been high for both men. In the post-Sept. 11 period, the administration has said that progress on the Israeli-Palestinian issue is important to help damp Islamic anger toward the United States.
As the U.S. struggled first with the unpredictability of Yasser Arafat's sunset years and the turmoil that followed his death 14 months ago, Bush continued to back Sharon as the Israeli prime minister built a West Bank barrier and withdrew from the Gaza Strip.
Sharon, often irascible and prickly, dictated the timing and conditions last summer of his actions in removing Israeli forces from Gaza and dismantling 21 Jewish settlements there and four others in the West Bank.
It was the first significant move during the Bush presidency toward the two-state solution the administration has advocated.
"He's been a pain in the neck, but an essential pain in the neck," said a senior Bush administration official who declined to be identified by name because his remarks were not authorized.
Added Quandt: "He knew what he was doing, knew where he wanted to go, and Bush was basically ready to back him."
But as a leader, Sharon has been a one-man show, unlike the late Yitzhak Rabin, who shared his own political gamble on the Oslo peace process in the mid-1990s with a politically powerful foreign minister, Shimon Peres. Rabin was assassinated in 1995.
Today, there is no strong Israeli successor for Bush to turn to.
The leadership capabilities of Sharon's No. 2, Olmert, are questionable, said many experts in Israeli politics. Olmert's vice premiership is due more to his relationship with Sharon than to voter appeal, and the new political party that Sharon founded, Kadima, could falter without Sharon.
Analysts said former Finance Minister Benjamin Netanyahu, the Likud Party standard-bearer who opposed Sharon's decision to turn Gaza over to the Palestinians, could be a prime beneficiary of Sharon's death or incapacitation. With general elections scheduled for March 28, the conservative Likud had plummeted in the polls after the prime minister's defection.
"Before Sharon's stroke ... the battle between Bibi and Sharon would have been fierce," said political analyst Hanan Kristal, using Netanyahu's nickname.
Olmert, in addition to assuming Sharon's prime ministerial powers, is the de facto leader of Kadima, at least for the time being. But he is not seen as having anything close to the ballot-box clout wielded by Sharon.
"The most important thing in coming days, assuming there's no miracle, is to ensure the continuing functioning of the country and the government," said Roni Bar-On, a veteran politician and senior figure in Kadima. "There are a number of people in Kadima from different disciplines -- defense, economy, law -- and any one of them could have been not only Sharon's No. 2, but also No. 1 for the party."
Kadima's platform calls for the creation of a Palestinian state alongside Israel, and many fear a loss of momentum toward that goal if Sharon is absent from the scene.
"Kadima without Sharon doesn't have legs," said Arthur Hughes, a former deputy assistant secretary of State for Near Eastern affairs now affiliated with the Middle East Institute, an independent Washington-based think tank.
Palestinian Authority President Mahmoud Abbas, who telephoned Olmert on Thursday to convey good wishes, said he was following news of the prime minister's health "with great worry."
Many Palestinians still harbor deep mistrust of Sharon even after the Gaza pullout, in large measure because of his baldly stated intention of retaining West Bank land on which several large Jewish settlement blocks lie. And some militant groups were openly gleeful over his collapse. One such organization, the Popular Resistance Committees, issued a statement hailing "the downfall of Dracula."
Traditionally, Israeli leaders with credentials and credibility as war heroes and political hawks -- such as Sharon and Rabin -- are the most successful at getting the Israeli public to go along with territorial concessions to the Palestinians.
A former aide to Rabin, Eitan Haber, said he found depressing parallels between the current situation and the aftermath of Rabin's assassination a decade ago by a young ultranationalist Jew.
"Every time there is a shred of hope, expectation, anticipation of progress [toward peace] ... we are dealt a blow that sends us back to the starting point," he told Army Radio.
Alluding to Sharon's decision to relinquish Gaza after years as the prime patron of the Jewish settlement movement, Haber said: "It is a bitter fate indeed if after someone changed his views so radically, and carried out this extraordinary, revolutionary move, we find ourselves back at square one."
Amid the developments, American policymakers face a hard reality they have long known: Sharon's imposing physical presence was also a metaphor for his political imprint.
"He is a huge and gigantic figure in Israeli politics, in the entire Middle East and in the world," Secretary of State Condoleezza Rice said Thursday at a breakfast with State Department reporters.
Without Sharon, the Bush administration finds itself in a defensive posture. Administration officials need to prevent any small incident from spinning out of control in the new climate of uncertainty and in the absence of strong leadership.
In a comment that conveyed a desire to carry on as best as possible, Rice said Thursday that there was no reason to delay Palestinian elections scheduled for Jan. 25, as Palestinian leaders have threatened.
"It's our view that they ought to be held and that people ought to campaign and put themselves on the line and try to convince the population that they will do better," Rice said.
But Sharon's departure is likely to curtail expectations for progress anytime soon on a crucial U.S. foreign policy priority.
Already, some diplomatic activity appeared to be on hold. Two senior U.S. envoys, National Security Council official Elliott Abrams and assistant secretary of State David Welch, were to have met with senior Israeli officials Thursday, but the talks were postponed.
"For the United States, it all means a time of waiting," said Edward Walker, president of the Middle East Institute and former ambassador to Israel and Egypt. "We can be an interested observer, but it will be difficult to affect the situation."
Marshall reported from Washington and King from Jerusalem.