Even so, Mr. Obama’s second term could offer a pivotal opportunity to restart the Israeli-Palestinian peace process. In his first term, he backed away from the process, figuring that America could mediate only if the parties themselves wanted to make peace — and that new talks were unlikely to be productive.

This is a mistake. The greatest enemy to a two-state solution is the sheer pessimism on both sides. Unless President Obama uses his new mandate to show leadership, the region will have no place for moderates — or for America either.

The rationale for inaction rests on four related assumptions: that strident forces dominate because their ideologies do; that the status quo — demographic trends that would lead to the enfranchisement of occupied Palestinians, a “one-state solution” and the end of Israel as a Jewish democracy — will eventually force Israel to its senses; that the observer-state status secured by Palestinian President Mahmoud Abbas at the United Nations is empty because his West Bank government is broke, dysfunctional and lacking in broad support; and that given the strength of the Israeli lobby, Mr. Obama’s hands are tied.

These assumptions seem daunting, but they are misguided. First, while Hamas, the militant Islamists who control Gaza, and Israel’s ultra-rightists, who drive the settlement enterprise, are rising in popularity, the reason is not their ideologies, but young people’s despair over the occupation’s grinding violence.

Last month, a poll by the S. Daniel Abraham Center for Middle East Peace, based in Washington, found that two-thirds of Israelis would support a two-state deal, but that more than half of even left-of-center Israelis said Mr. Abbas could not reach binding decisions to end the conflict. The same month, the Palestinian Center for Policy and Survey Research, in Ramallah, found that 52 percent of Palestinians favored a two-state resolution (a drop from three-quarters in 2006, before two Israeli clashes over Gaza). But two-thirds judged the chance of a fully functional Palestinian state in the next five years to be low or nonexistent. In short, moderates on both sides still want peace, but first they need hope.

Second, the status quo is not a path to a one-state solution, but to Bosnian-style ethnic cleansing, which could erupt as quickly as the Gaza fighting did last year and spread to Israeli Arab cities. Right-wing Israelis and Hamas leaders alike are pushing for a cataclysmic fight. Mr. Abbas, whose Fatah party controls the West Bank, has renounced violence, but without signs of a viable diplomatic path he cannot unify his people to support new talks. If his government falls apart, or if the more Palestinian territory is annexed (as right-wing Israeli want), or if the standoff in Gaza leads to an Israeli ground invasion, bloodshed and protests across the Arab world will be inevitable. Such chaos might also provoke missiles from Hezbollah, the Iranian-backed Shiite militant group based in Lebanon.

Third, the Palestinian state is not a Fatah-imposed fiction, but a path toward economic development, backed by international diplomacy and donations, that most Palestinians want to succeed. It has a $4 billion economy; an expanding network of entrepreneurs and professionals; and a banking system with about $8 billion in deposits. A robust private sector can develop if given a chance.

Fourth, American support need not only mean direct talks. The administration could promote investments in Palestinian education and civil society that do not undermine Israeli security. Mr. Obama could demand that Israel allow Palestinian businesses freer access to talent, suppliers and customers. He could also demand a West Bank-Gaza transportation corridor, to which Israel committed in the 1993 Oslo accords.

America is as much a player as a facilitator. The signal it sends helps determine whether the parties move toward war or peace. The White House, despite its frosty relationship with Mr. Netanyahu, hasn’t set itself up as a worthy mediator by opposing Palestinian membership in the United Nations and vetoing condemnations of settlements.

In nominating Chuck Hagel to lead the Pentagon, Mr. Obama rightly ignored attacks by “pro-Israel” (really pro-Netanyahu) groups. He should appoint a Middle East negotiator trusted by all sides — say, Bill Clinton or Colin L. Powell. He should lead, not thwart, European attempts to make a deal. He has stated that the settlements will lead to Israel’s global isolation; he should make clear that they endanger American interests, too.

Washington has crucial leverage, though this won’t last forever. When it weighs in, it becomes a preoccupying political fact for both sides. If it continues to stand back, hopelessness will win.