President Bush is frustrated, his ambassador to Baghdad is disappointed. But there are no ready alternatives to Iraqi Prime Minister Nouri al-Maliki, and his opponents lack the votes to replace him.

What’s more, the country remains so fractured along sectarian and ethnic lines that it’s doubtful whether any other politician could do a better job under Iraq’s current system.

Such is the sobering reality facing the Bush administration three weeks before a watershed report to Congress on the state of Iraq after this year’s U.S. troop buildup. The White House can point to progress at calming violence in Baghdad and other parts of the country. But the Bush administration cannot paper over the failure of al-Maliki’s government to forge unity among the country’s main groups: Shiites, Sunnis and Kurds.

Without some type of three-way accord, U.S. commanders warn that the recent military gains cannot be sustained.

Trying to read Bush’s views on al-Maliki has become more complicated.

On Wednesday, he told a veterans’ convention that the Iraqi leader is “a good man with a difficult job and I support him.”

A day earlier, however, Bush caused a stir by acknowledging reservations about the Shiite prime minister’s performance, citing “a certain level of frustration” with him.

“If the government … doesn’t respond to the demands of the people, they will replace the government,” Bush said Tuesday. “That’s up to the Iraqis to make that decision, not American politicians.”

Meanwhile in Baghdad, U.S. Ambassador Ryan Crocker was telling reporters that political progress has been “extremely disappointing and frustrating to all concerned – to Iraqis, to the Iraqi leadership itself.”

Sen. Carl Levin, chairman of the U.S. Senate Armed Services Committee, took the complaints even further, urging the Iraqi parliament to oust al-Maliki and replace him with someone less sectarian.

Hillary Rodham Clinton, the 2008 Democratic presidential front-runner, echoed the call in a statement Wednesday, saying the parliament should find a “less divisive and more unifying figure” to reconcile political and religious factions.

Ousting al-Maliki, a longtime Shiite political activist, would require a majority vote in the 275-member Iraqi parliament. As long as the Kurdish parties and the main Shiite bloc stand beside al-Maliki, his opponents lack the votes despite some recent defections by smaller parties.

Some of the remaining Shiite and Kurdish support for al-Maliki is based on fear of what might happen if he were to go. Under the constitution, the entire Cabinet would have to be dissolved, and all ministries would be up for grabs.

Deciding who would get the nearly 40 Cabinet-level posts could take months, paralyzing the government and perhaps jeopardizing recent security gains.

That is as unpalatable a prospect for U.S. policymakers as it is frightening for many Iraqis.

Al-Maliki himself is unlikely to give up without a fight. He told reporters Wednesday in Damascus, Syria, that he would “pay no attention” to his American critics and if necessary “find friends elsewhere.”

A few names have been circulated as alternatives, notably former Prime Minister Ayad Allawi, a secular Shiite favored by some of Iraq’s Sunni Arab neighbors. Also on the short list: Vice President Adil Abdul-Mahdi, a member of a Shiite religious party.

But each has strong negatives. Allawi, whose previous administration was tainted by corruption, is mistrusted by Shiite religious parties. Abdul-Mahdi has twice failed to win a Shiite endorsement. In addition, neither has enough following in parliament to depose al-Maliki, who took office in May 2006.

“The problem isn’t just al-Maliki, it’s the job,” said Jon Alterman of the Center for Strategic and International Studies, a Washington think tank.

From the early days of its role in Iraq, the United States pushed for a broadly inclusive government, Alterman noted. Instead, the government fell under the influence of hard-line Shiite factions with little interest in compromise – distrusted by Sunnis and only tolerated by the Kurds.

U.S. officials have long understood the problem. But the same mistrust and rivalry that have prevented political reconciliation have also blocked efforts to forge a new alliance.

For nearly a year, the Americans have been encouraging key figures from the Sunni, Shiite and Kurdish parties to come together in a new “coalition of the moderates” to bolster al-Maliki – or, if necessary, replace him.

Last week, moderate Shiites and Kurds announced a new alliance but failed to persuade any Sunni parties to join them. And without the Sunnis, who are deeply suspicious of al-Maliki, the new alliance means little.

Kenneth Pollack, a Mideast expert at the Brookings Institution, believes the only way out is for the United States to push for new national elections to replace a parliament that is “completely dominated by Shiite warlords.”

But there is no way that can happen fast enough to satisfy U.S. critics in Congress – who are pressing for a speedy withdrawal of U.S. military forces.

“The foundation of this (system of) government is so rotten, it’s hard to see how it can be salvaged,” Alterman said.