ST. PETERSBURG, Russia -- President Barack Obama scrambled with senior advisers Thursday to soften resistance to a military strike against the Syrian government among U.S. lawmakers and some of the president's most reliable global allies.
Mr. Obama has staked the credibility of the United States -- and his presidency -- on his call for a military operation to punish the Syrian government for its alleged use of chemical weapons against civilians last month.
But the president faces hardening barriers in Congress, where both Republican critics and Democratic allies have voiced deep reservations or flat opposition to his proposal to enter another war in a predominantly Muslim nation after more than a decade of U.S. conflict overseas. Polls show that much of the American public is skeptical, too.
Mr. Obama carved out time from his trip abroad this week to call key U.S. lawmakers personally, including five calls to Democratic and Republican senators Wednesday.
The urgency partly reflects the surprising way that Mr. Obama culminated days of deliberation over how to respond to President Bashar Assad's alleged use of chemical weapons, which Mr. Obama called "an assault on human dignity" that cannot go unpunished. He announced Saturday that he would seek congressional approval for any military strike against the Syrian government, and he has struggled to rally support across party lines amid his previously scheduled trip to Sweden and Russia.
The White House lobbying effort has included direct conversations between Mr. Obama or top administration officials and at least 60 senators and at least 125 House members as of Thursday, according to a White House official, who spoke on condition of anonymity to discuss internal administration operations.
Late Thursday afternoon, Vice President Joe Biden and deputy national security adviser Tony Blinken briefed a bipartisan group of House and Senate members in the White House Situation Room on Syria, an administration official said.
The congressional vote's outcome, especially in the Republican-led House, is unclear, and the issue has blurred traditional party lines.
White House officials said they are not concerned about the vote trend in Congress so far. They said Mr. Obama, who returns to Washington late today, will begin a more public campaign, including perhaps a presidential address, to win support for a strike from Congress and the American public.
The full Senate plans to begin considering as early as today a resolution authorizing the use of force, after a divided Foreign Relations Committee this week backed limited military action. Senate Majority Leader Harry Reid, D-Nev., is "guardedly optimistic" that the resolution can pass, according to Senate aides.
But Sen. Joe Manchin III, D-W.Va., who has been a bipartisan consensus-builder, said Thursday that a military strike "would be the wrong course of action" before all diplomatic options are exhausted.
Here in St. Petersburg, Mr. Obama's quandary over Syria -- and his estrangement from the summit's host and key Syria patron, Russian President Vladimir Putin -- largely overshadowed the economic agenda of the Group of 20 meeting.
Mr. Obama used the gathering to privately press his G-20 colleagues to support a U.S.-led strike in words, if not resources. He found one possible ally in Japanese Prime Minister Shinzo Abe, who Mr. Obama said agrees that the Syrian attack should not go unpunished.
The White House detailed an extensive outreach to lawmakers that is being coordinated by aides in Washington, as well as by National Security Adviser Susan Rice and a key deputy, Benjamin Rhodes, who are traveling with Mr. Obama in Russia.
On Wednesday, Mr. Obama and senior White House officials made more than 25 phone calls to lawmakers from both parties. Chief of Staff Denis McDonough arranged calls with the Progressive Caucus and the Hispanic Caucus in the House, while Mr. Blinken held a conference call with Jewish House members.
The administration also has held classified briefings for any lawmaker who requests one detailing evidence that the alleged Aug. 21 chemical attack was carried out by Mr. Assad's regime. The administration has said more than 1,400 civilians, including at least 426 children, were killed when rockets containing highly toxic sarin gas were launched from regime territory and landed on rebel strongholds or contested areas in the Damascus suburbs.
Secretary of State John Kerry and Defense Secretary Chuck Hagel have participated in the Capitol Hill outreach, as has Mr. Biden. Samantha Power, the U.S. ambassador to the United Nations, said Thursday that the United States must "respond decisively to this horrific attack" in Syria.
Mr. Obama spent most of the day Thursday in private meetings with world leaders, but spoke briefly with reporters at the start of one session. Seated at a long table across from Mr. Abe, Mr. Obama spoke about their "joint recognition that the use of chemical weapons in Syria is not only a tragedy, but also a violation of international law that must be addressed."
The loudest critic of military action in Syria is Mr. Putin, who has scoffed at U.S. allegations about the attack. Mr. Putin welcomed Mr. Obama to the ornate Constantine Palace, once the summer playground for Russian czars, with a formal handshake and about 15 seconds of chitchat. The two leaders do not plan to meet here, although U.S. officials said Mr. Obama and Mr. Putin may interact informally on the summit's sidelines.
Mr. Obama has argued forcefully that a U.S.-led military strike is needed to enforce an international ban on use of chemical weapons and to degrade the ability of Mr. Assad's forces to use them again in a brutal conflict with rebels that is in its third year.
The State Department said Thursday that Mr. Kerry, the administration's most visible supporter of military action in Syria, will travel to Europe over the weekend for consultations with allies and partners. He is scheduled first to speak with European Union counterparts meeting in Lithuania. In Paris, Mr. Kerry will meet with senior French officials and with Arab League representatives.
In Washington, many lawmakers said they were unconvinced that the United States should engage militarily in Syria, even after national security officials' closed-door classified briefings.
"I've had more phone calls on this issue than on any issue I've ever had since I got here in 2001, and my phone calls, e-mails, faxes are running 96 percent now," said Rep. John Abney Culberson, R-Texas. He said there's "absolutely no question" that Mr. Assad attacked innocent civilians, but that "America has absolutely no strategic interest involved, and we should stay out of it."
A growing number of liberals also oppose military action, including key allies of House Minority Leader Nancy Pelosi, D-Calif., who backs a strike.
With a House vote several days away, at least, aides said Ms. Pelosi has not started reaching out to individual lawmakers because she believes that colleagues need time to review hundreds of classified documents and other materials.