WASHINGTON — The White House faces the strong possibility of a defeat over Syria that could seriously damage the president for the rest of his tenure, a peril the administration will battle this week as members of Congress return to work and open a decisive chapter of the Obama presidency.
Administration efforts to seek support from lawmakers, including personal phone calls by the president, so far appear to have changed few minds.
Nor has the support of top Republican and Democratic congressional leaders in both houses, who have lined up behind President Obama's plan to punish the government of Syrian President Bashar Assad for what U.S. officials say was a poison gas attack last month near Damascus that killed more than 1,400 people.
Administration officials say they remain optimistic about winning a vote in the Senate, expected later this week. Vice President Joe Biden hosted Obama and six GOP senators for dinner at the vice presidential residence Sunday night.
But even in the Senate, the result remains in doubt and may require Biden to break a tie vote. And in the House, the support of Speaker John A. Boehner (R-Ohio) and Minority Leader Nancy Pelosi (D-San Francisco) has not swayed an impromptu liberal-conservative alliance that opposes the Syria plan.
The president faces a potent dual threat — Republicans who don't trust and won't support him despite the urgings of their leadership and a sizable antiwar contingent of Democrats who oppose military action except for national self-defense. Public opposition to the proposed cruise missile strikes against Syria has bolstered those lawmakers.
Congressional and White House aides cautioned against drawing "premature" tallies of the votes, because many lawmakers are just considering the issue as they return from the monthlong summer recess.
But the nature of the White House lobbying, heavily focused on groups who are ordinarily among the president's strongest supporters, highlights how difficult Obama's position has become. Officials plan to bus members of the Congressional Black Caucus to the White House on Monday so national security advisor Susan Rice can personally urge them to support military action in Syria. Several members of the caucus already have publicly opposed a military strike.
Pelosi has nudged her troops almost daily. A letter Saturday suggested they consider the work of Sen. Barbara Boxer (D-Calif.), a liberal ally, who voted to approve the Syria resolution in the Senate Foreign Relations Committee.
The White House is well accustomed to losing legislative battles because of Republican opposition. But large-scale defections among Democrats would create a high-profile, bipartisan rebuke of a president's foreign policy wishes, a move that has little precedent.
To try to avoid that, Obama plans to step up his personal efforts, blanketing the airwaves with a series of television interviews Monday and a speech to the nation and a visit to Capitol Hill to meet Senate Democrats on Tuesday.
Obama plans to emphasize several key points, according to a senior administration official who requested anonymity in discussing White House strategy: Officials have no doubt Assad is responsible for the sarin gas attack, a military strike would be limited, the U.S. has exhausted all diplomatic channels, and it is up to the U.S. to act.
The messaging blitz might not move poll numbers, the official said. But it is aimed in part at lawmakers who have wanted the president to own the case for action.
Meantime, Assad, in a rare interview, sent his own message, warning against military involvement by the United States.
CBS News said Sunday that in the interview Assad threatened that "people aligned with him" would retaliate against the U.S. for any attack and denied using chemical weapons. The network plans to air the interview Monday; interviewer Charlie Rose previewed its contents Sunday on "Face the Nation."
Administration officials said that they had spoken to at least 85 senators and more than 165 House members in the last two weeks, an unusual accounting of its behind-the-scenes lobbying that implicitly acknowledged the stakes of the fight that none of Obama's advisors expected and some argued against having.
But the conversations so far have had limited effect. One undecided House Democrat from a moderate district entered the week wary but looking for a reason to support the president, said an aide who asked for anonymity in discussing the lawmaker's thinking.
A week of briefings and a review of the administration's case left the lawmaker only more convinced that the administration could not promise the "limited" intervention Obama has described.
With the congressional midterm reelection fight around the corner, the lawmaker would need a powerful reason to defy the clear message coming from constituents.
"All we're hearing is no," the House aide said of the calls coming to the congressional office.
In addition to its efforts with Democrats, the White House is enlisting former Bush administration officials and Republican foreign policy experts to appeal to GOP lawmakers. However, the vote count so far has illustrated not just Obama's weakness on Capitol Hill but also stark divisions among Republicans.
The onetime GOP unity on foreign affairs has splintered, with the party's anti-interventionist wing growing in strength. The more traditional hawks appear unable to influence the newer libertarians.
The unusual left-right partnership was evident Sunday as Sen. Ted Cruz (R-Texas), a tea party champion, cited Dennis Kucinich, a favorite of the Democratic left wing, as the source for his suggestion that a cruise missile attack on Assad's government would turn the U.S. into "Al Qaeda's air force."
The reality that some of the rebel groups fighting Assad have links to Al Qaeda is one of several issues that lawmakers of both parties, even those inclined to back Obama, have wrestled with.
In the Senate, only a handful of Republicans, led by Sen. John McCain (R-Ariz.), have said they will support military action against Syria.
Failure to win congressional approval of a strike against Syria, which Obama abruptly decided to pursue a week ago, could harm his second-term agenda not only in foreign affairs, but in domestic policy as well. Budget issues and immigration reform, his top domestic priority, are pending in Congress.
"If Congress won't support him on this, they'll be much more willing to say no," said Julian E. Zelizer, a professor of history and public policy at Princeton University.
"It will signal that Obama can't move Congress," he said, and "just as troublesome, it will show again that the Republican leadership can't control its caucus, and liberal Democrats are no longer willing to stand behind him out of loyalty."
On Sunday, the administration sent White House Chief of Staff Denis McDonough onto all five network public affairs talk shows to make the case for the Syria policy, hoping he would accomplish more than Secretary of State John F. Kerry did with a similar set of television appearances a week earlier.
"The question for Congress this week is a very simple one: Should there be consequences for his having used gases, chemical weapons, to kill more than 1,000 of his own people, including more than 400 children?" McDonough said. U.S. failure to act would encourage Iran, Hezbollah and other U.S. adversaries, he said.
Rep. Adam Kinzinger (R-Ill.), an Air Force pilot during the Iraq and Afghanistan wars who supports striking Syria, expressed his frustration with Congress and the White House.
"But this is a moment in time where I think in 10, 20, 30 years, the history books are going to say this was a redefining moment in world history, and what was the United States doing?"
Times staff writer Paul Richter contributed to this report.