


Mr. Obama's top challenge, as Congress returns Monday from summer recess, will be to find backing from enough lawmakers for a resolution authorizing a strike. He faces an unusual alliance seeking to block military action, one comprised of the president's closest allies among liberal Democrats—including members of the Congressional Black Caucus—and his most strident critics among Republicans.

Timeline: Punitive Strikes

U.S. military action against Syria likely would join a growing list of instances in which the U.S. has fired Tomahawk cruise missiles.

The administration's argument is that the U.S. case that Mr. Assad's forces used chemical weapons in the Aug. 21 attack is now settled—an assertion that Mr. Assad denied in an interview with Charlie Rose of PBS and CBS.


"We are no longer debating whether it happened or whether it didn't happen," White House Chief of Staff Denis McDonough said on CNN, part of a blitz of television interviews Sunday. "Congress has an opportunity this week to answer a simple question: Should there be consequences for him for having used that material?"

Mr. Obama will also go to Capitol Hill Tuesday to meet with Senate Democrats, a Senate Democratic aide said.

The Senate is expected to vote this week on a resolution authorizing Mr. Obama to use force in Syria. The current resolution, which could be amended, backs a military mission designed, in part, to change the momentum of the Syrian civil war and set the stage for Mr. Assad's departure.

Syria in the Spotlight


But it isn't clear whether Congress—particularly the House, where Mr. Obama faces a more ominous battle—will back such a measure. Many lawmakers have said they oppose the resolution as too broad, and their contention likely was bolstered during the recess as they heard constituents back home voice concern. The House isn't expected to vote before next week.

After a week of intense White House lobbying on Capitol Hill following Mr. Obama's surprise decision to seek authorization from Congress for a military strike, some lawmakers say they remain unsure who was responsible for the alleged chemical-weapons attack or remain unconvinced a strike would be the appropriate response.

Liberal Democrat Rep. Jim McGovern (D., Mass.) suggested the president withdraw the resolution. "I don't believe the support is there in Congress," he said on CNN.

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With Syrian refugee numbers passing the two million mark, review some aerial views of camps in Jordan, Turkey and Iraq.

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Even those who have said they back a resolution express concern about the president's ability to pull off a successful vote. "It's an uphill slog from here," House Intelligence Committee Chairman Mike Rogers (R., Mich.) said Sunday on CBS, calling the administration's lobbying of lawmakers belated.

Mr. Rogers said the president should have called Congress back for a debate over Syria instead of leaving the country for the G-20 meetings last week in Russia. "It's very clear he's lost support in the last week," Mr. Rogers said.


Secretary of State John Kerry, in Paris to build support for strikes on Syria, grabs a seat for a meeting with other U.S. diplomats at the Tuileries Garden. Susan Walsh/Press Pool

The White House has left open the possibility that Mr. Obama would proceed with military action if a vote in Congress fails. Administration officials also haven't ruled out presidential action if the House and Senate pass different resolutions yet are unable to agree on a compromise measure, but say it is too early to consider such a scenario.

Adding to Mr. Obama's challenges, Mr. Assad waded into the debate by denying in the interview with Mr. Rose that he had anything to do with the alleged chemical-weapons attack and saying he didn't even know whether one had taken place.

Mr. Assad refused to say whether Syria has chemical weapons, but he said any weapons would be under government control, Mr. Rose said in describing the interview that is scheduled to air Monday. At the same time, Mr. Assad repeated his suggestion that the Syrian opposition may have been behind the alleged attack, a charge the U.S. and opposition leaders deny. Additionally, Mr. Assad suggested there would be a response if the U.S. launches a strike, Mr. Rose said.

Part of the White House effort to persuade Congress to approve a strike includes trying to show that the president has a cadre of international support. U.S. Secretary of State John Kerry met with members of the European Union and Arab League over the weekend, and said that both groups support parts of the U.S. position. Neither, however, has explicitly endorsed U.S. military strikes.

Many lawmakers returning to Washington will attend their first classified briefings on Syria this week, raising hope among administration officials that intelligence information will sway undecided members. They likely will be shown graphic videos detailing the effects of the alleged chemical attack on victims.

Most lawmakers remain publicly undecided, while many Republican lawmakers have said they are leaning toward opposing military action. "The president has not made his case," one of them, Rep. Marsha Blackburn (R., Tenn.) said on CNN.

A strike is backed by both House Speaker John Boehner (R., Ohio) and House Majority Leader Eric Cantor (R., Va.).

The White House could get another boost from the American Israel Public Affairs Committee, an influential pro-Israel lobbying group that supports Mr. Obama's plans. The group is expected to meet with more than 300 lawmakers this week, according to an AIPAC official.

Underscoring the stakes for his presidency, Mr. Obama has done the kind of personal outreach to lawmakers he has been criticized for eschewing since taking office.

Administration officials say they have reached out to at least 85 senators and more than 165 House members. Vice President Joe Biden hosted a dinner Sunday night with a group of Republican senators that Mr. Obama attended. On Monday Mr. Kerry, Defense Secretary Chuck Hagel and National Security Adviser Susan Rice are scheduled to brief House members on U.S. intelligence assessments.

Mr. Obama's high-stakes gamble to win congressional backing—after he was on the brink of launching a strike unilaterally—could lead to a humiliating defeat and deplete the president's political capital as he turns to pushing his domestic agenda through Congress.

But the prospect of the president losing the Syria vote is so worrisome to some lawmakers—even some who oppose a strike—that the White House eventually may win support because of a desire to avoid the international humiliation of Congress rejecting the president.

—Janet Hook contributed to this article.

Write to Carol E. Lee at carol.lee@wsj.com and Kristina Peterson at kristina.peterson@dowjones.com