Like so many of his predecessors, President Obama is quickly discovering that persuading Israel to change course is nearly impossible.

Obama came to office determined to achieve a two-state solution between Israelis and Palestinians. His opening move was to insist that Israel stop building settlements in the West Bank and East Jerusalem -- a tough line aimed at bolstering Palestinian President Mahmoud Abbas and persuading key Arab states to make conciliatory gestures toward Israel. These steps would pave the way for the creation of a viable Palestinian state and the normalization of Israel's relations with its Arab neighbors, and also help rebuild America's image in the Arab and Muslim world.

Unfortunately, Israeli Prime Minister Binyamin Netanyahu has no interest in a two-state solution, much less ending settlement expansion. He and his government want a "greater Israel," which means maintaining effective control of the West Bank and Gaza. His response to Obama's initiative has ranged from foot-dragging to outright defiance, with little pushback from Washington.

This situation is a tragedy in the making between peoples who have known more than their share. Unless Obama summons the will and skill to break the logjam, a two-state solution will become impossible and those who yearn for peace will be even worse off than before.

Netanyahu initially claimed in early June that the Bush administration had assured Israel that "natural growth" of the existing settlement blocs was permissible -- an assertion that Secretary of State Hillary Rodham Clinton and other officials promptly denied. Netanyahu further declared that 2,500 housing units under construction would be completed. He then made a minor concession after Obama's June address to the Muslim world in Cairo, slipping a single reference to a "demilitarized Palestinian state" into an otherwise uncompromising speech at Bar-Ilan University. The onerous conditions that Netanyahu demanded of such a state made it clear that he was merely tossing Obama a bone to avoid clashing with a then-popular U.S. president.

Netanyahu's stance hardened as Obama's approval ratings slipped. In July, after U.S. officials tried to halt an Israeli plan to convert an old Arab hotel into 20 Jewish apartments in Sheik Jarrah -- an Arab neighborhood in East Jerusalem -- Netanyahu told his Cabinet that "Jerusalem is not a settlement, and there is nothing to discuss about a freeze there." Underscoring the point, Israeli authorities expelled two Arab families in Sheik Jarrah from homes they had inhabited for 50 years.

Then last month, an unnamed "senior U.S. official" told reporters that peace talks might resume without an agreement to halt all settlement construction, and Netanyahu reiterated that he opposed a complete freeze. A few days later, Israel authorized construction of hundreds of additional housing units in the West Bank. In response, the White House merely said that it "regretted" this action, adding that the "U.S. commitment to Israel's security is and will remain unshakeable." Three days later, the Israel Lands Administration issued tenders for 468 new apartments in East Jerusalem. And just a week ago, Netanyahu announced that a complete freeze on settlement building "will not happen" and that construction in Jerusalem "would continue as normal."

Why is Netanyahu defying Obama so openly? Because he has long been committed to the dream of a "greater Israel," and the only Palestinian state he might accept would be an archipelago of disconnected enclaves under de facto Israeli control. His Cabinet is even more hard-line, which means his government would collapse if he made meaningful concessions. Furthermore, attempting to remove a substantial portion of the 300,000-plus settlers living in the West Bank could trigger a violent reaction within Israel, possibly even putting Netanyahu at risk of suffering the fate of former primer minister Yitzhak Rabin, who was assassinated by a Jewish extremist in 1995.

Some observers say that Netanyahu's decision to authorize new housing units is merely a sop to his right-wing colleagues and that he will eventually agree to a temporary freeze on settlements and serious negotiations with the Palestinians. But even if he does, history suggests that any pledge to stop settlement expansion would be meaningless. Previous Israeli governments also promised to halt settlement building, most recently in the 2003 "Road Map" agreement that set a formal timetable for Middle East peace. Yet despite these promises, the number of settlers has more than doubled since the early 1990s and has grown by about 5 percent annually since Israel formally accepted the "Road Map" in May 2003.

Nor is settlement expansion the work of a handful of rebellious religious extremists. Labor and Likud governments have backed this enterprise with economic subsidies, essential infrastructure and military protection, as well as an array of roads, checkpoints and security barriers. In demanding a freeze, Obama is attempting to get Israel to halt a project that its major political parties have pursued for more than 40 years. And even though Israel receives more than $3 billion each year from the United States, his efforts to halt expansion and achieve a two-state solution will probably fail.

Why is Obama letting Netanyahu thwart his efforts? To begin with, the president has too much on his plate -- the economic crisis, the health-care battle, Afghanistan, Iran's nuclear problem -- so the attention he can devote to Israeli-Palestinian peace is limited.

And then there is the Israel lobby. The good news is that there is a new pro-Israel organization, J Street, which is committed to the two-state solution and firmly behind Obama. The bad news is that the American Israel Public Affairs Committee (AIPAC) and other defenders of the status quo remain powerful, and they will surely oppose any attempt to pressure Netanyahu. In May, for example, AIPAC drafted a letter warning Obama to "work closely and privately" with Israel. It garnered 329 signatures in the House and 76 names in the Senate. During the August recess, 56 members of Congress visited Israel, and House Majority Leader Steny H. Hoyer (D-Md.) told reporters that it was a mistake to make settlement construction the key issue and that there was a "significant difference" between settlements in the West Bank and those in East Jerusalem.

If Obama tries to make aid to Israel conditional on a settlement freeze, Congress will simply override him. Putting real pressure on Israel risks alienating key politicians and major Democratic fundraisers, as well as Israel's supporters in the media, imperiling the rest of Obama's agenda and conceivably his prospects for reelection. Moreover, several of Obama's top advisers, such as Dennis Ross, are enthusiastic supporters of America's "special relationship" with Israel and would almost certainly oppose using U.S. leverage to force Israeli concessions. Obama and special envoy George Mitchell are negotiating with one hand tied behind their backs, and Netanyahu knows it.

If tangible progress toward a viable Palestinian state does not happen soon, however, Abbas and other moderate Palestinians will only be weakened and radical groups such as Hamas only strengthened. Obama's commitment to two states for two peoples, and his declaration in Cairo that "it is time for these settlements to stop," will sound hollow. Israel will be stuck repressing millions of angry Palestinians and will increasingly resemble an apartheid state. As former prime minister Ehud Olmert put it in 2007, failure to achieve a two-state solution will force Israel into a "South-African style struggle." And if that happens, he warned, "Israel is finished."

Obama said in Cairo that a two-state solution is "in Israel's interest, Palestine's interest, America's interest and the world's interest." He's right, but it's not the rest of the world that needs to get behind this vision. It is the Israelis who have to be convinced, and that will take sustained U.S. pressure. To succeed, Obama must use his bully pulpit to explain to the American people that the two-state solution is by far the best outcome for Israel and that time is running out. If he does not get that message across, he will become the latest in a long line of U.S. presidents who tried to end this conflict -- and failed.

Stephen M. Walt, professor of international affairs at Harvard University, is co-author of "The Israel Lobby and U.S. Foreign Policy" and a contributing editor of Foreign Policy magazine.