The past four Israeli elections have been won by a candidate who promised to end Israel's conflict with the Palestinians. Tomorrow, for the first time in decades, Israelis may choose a prime minister who is promising to wage war.

"We must smash the Hamas power in Gaza," Likud party leader Binyamin ("Bibi") Netanyahu said at one rally last week. "There will be no escape from toppling the Hamas regime," he said at a security conference the next day. "I'm sorry to say we haven't gotten the job done," he said of Israel's recent Gaza offensive in a radio interview. "The next government will have no choice but to finish the job and uproot . . . the Iranian terror base."

Perhaps Netanyahu won't win -- he's only narrowly ahead of Foreign Minister Tzipi Livni, who is promising to continue peace talks. Maybe he won't act on his words; campaign rhetoric is campaign rhetoric. But the Obama administration faces the very real prospect of having to manage the most volatile and contentious relationship with Israel since a decade ago, when Israel's prime minister was. . . . Bibi Netanyahu.

It's not just the possibility that a Netanyahu-led government would seek to "topple" Hamas -- something that would require another, even bloodier Israeli invasion and leave its army stuck in the territory indefinitely. Netanyahu is also saying a top priority will be "harnessing the U.S. administration to stop the threat" of Iran's nuclear program -- something he strongly suggests would require military action. He advocates putting Israeli-Palestinian peace talks on hold indefinitely and says he will not stop the expansion of Jewish settlements. He has never endorsed the creation of a sovereign Palestinian state, and he says he will not support Israeli withdrawal from the Golan Heights -- the key to any peace deal with Syria. One possible coalition partner, now surging in the polls, is Avigdor Lieberman, a far-right leader who advocates harsh discrimination against Israel's Arab minority.

In short, just at the moment that a new U.S. administration launches a policy aimed at addressing the multiple conflicts of the Middle East with intensive diplomacy, it may find itself with an Israeli partner that rejects negotiations with its neighbors and does its best to push the United States toward military confrontation with Iran and its proxies.

If history is any indication, Netanyahu won't be shy about pursuing his agenda in Washington. Following his first election, in 1996, he "was overcome by hubris," Dennis Ross, then and now a principal in the administration's Mideast diplomacy, recounts in a book he published in 2004. After Netanyahu's first meeting with President Bill Clinton, Ross wrote, "Clinton observed: 'He thinks he is the superpower and we are here to do whatever he requires.' " Over the next several years, Netanyahu -- with plenty of help from Yasser Arafat -- slowly strangled the Oslo accords, the most promising Israeli-Palestinian deal ever struck. He turned every step of the process into an excruciating ordeal, while all the time seeking to mobilize pro-Israel pressure on Clinton by Congress, the American Jewish community and even evangelical Christians. When Israelis voted him out of office, in 1999, they did so in part because he was perceived to have poisoned relations with the country's indispensable ally.

So will Bibi do it again? Maybe not: His supporters say Netanyahu has learned from his previous term. He has said he hopes to form a broad centrist government; arguably, there is much such a government and the Obama administration could agree about. Netanyahu has proposed a campaign to build up the West Bank economically, an idea that fits with the U.S. strategy of bolstering the Palestinian Authority under President Mahmoud Abbas. The outgoing government of Ehud Olmert is reportedly close to striking a deal with Hamas on a cease-fire, which would constrain the next prime minister. In any case, Netanyahu probably would not launch an invasion of Gaza if the White House strongly opposed it.

Still, it's worth passing on Ross's recollection of the last Israeli election night in which Netanyahu figured, on May 17, 1999. As Ross tells it in "The Missing Peace," Abbas was staying at the Ritz-Carlton in Pentagon City, and the two men agreed to watch the returns together. When Ross arrived, Abbas greeted him by saying: "Either we toast the outcome or we jump out the window together." Netanyahu lost in a landslide, but Ross warned the jubilant Abbas, "In Israeli politics never say never . . . if there is a catastrophe [Netanyahu] can come back." You have to wonder if the Palestinian president and the Obama administration's new Middle East counselor will be standing by their windows tomorrow night.