The White House laid out an intense week of lobbying, with Obama addressing the nation from the White House Tuesday night.
"I did not put this before Congress just as a political ploy or as symbolism," Obama said, adding that it would be a mistake to talk about any backup strategy before lawmakers vote on a use-of-force resolution.
The president spoke to reporters at the end of a two-day international summit, where he sought backing for a strike against Syria in retaliation for a deadly chemical weapons attack against civilians. But Obama appeared to leave the summit with no more backing than he had when he arrived.
In fact, Russian President Vladimir Putin, a staunch ally of Syrian President Bashar Assad, said he was the one with support from the majority of countries attending the Group of 20 meeting. Putin insisted anew that Obama seek approval from the United Nations before taking military action, despite the fact that Russia has blocked previous Security Council efforts to punish Assad throughout Syria's bloody 2½-year civil war.
The White House tried to counter Putin's assessment by releasing a joint statement from the U.S. and 10 other countries announcing support for "efforts undertaken by the United States" to enforce an international prohibition on chemical weapons use. The statement did not specify military action against Syria, but administration officials said the intent was to show international support for that type of response.
The countries signing the statement with the U.S. were Australia, Canada, France, Italy, Japan, South Korea, Saudi Arabia, Spain, Turkey and the United Kingdom.
Putin said the U.S. push for military action has been supported only by Turkey, Canada, Saudi Arabia and France.
"The use of force against a sovereign nation is only possible as self-defense - and Syria hasn't attacked the United States - and on approval of the U.N. Security Council," Putin said. "Those who do otherwise place themselves outside the law."
Indeed, Obama's coalition appeared anything but strong. Britain's Parliament has already voted against military action. Even French President Francois Hollande, who has expressed willingness to form a military coalition with the U.S. against Syria, displayed sudden caution, saying he would wait until a United Nations investigation into the Aug. 21 sarin gas attack was released before deciding whether to intervene militarily. The U.N. report is not expected to be released until mid-to late-September.
Obama and Hollande discussed strategy during a meeting on the sidelines of the summit Friday. The U.S. president also held a surprise meeting with Putin. The two leaders, who have a strained relationship, said their conversations were candid, but yielded no new agreement on Syria.
The burden of undertaking military action appeared to be weighing on Obama throughout his 50-minute post-summit question-and-answer session. He made several references to the immense responsibility the world places on the United States in responding to humanitarian crises, saying that the first question often asked is, "Why isn't the United States doing something about this?"
The president departed Russia Friday night, bound for Washington where he also faces tough going in rallying support for military action, including from fellow Democrats. Force-authorization resolutions face an uncertain future in Congress, and a significant segment of the American public opposes a strike.
In addition to Obama's Tuesday night speech, administration officials scheduled new classified briefings for lawmakers and White House chief of staff Denis McDonough was making the rounds on all five Sunday talk shows.
The president admitted his campaign may not succeed.
"It's conceivable at the end of the day I don't persuade a majority of the American people that it's the right thing to do," he said. "And then each member of Congress is going to have to decide."
The options facing the U.S. and the international community are neither convenient nor appetizing, Obama said. But he appealed for action on moral grounds, citing U.S. estimates that the chemical weapons attack killed more than 1,400 people, including 426 children. Other estimates are somewhat lower.
"There are times where we have to make hard choices if we're going to stand up for the things that we care about," he said. "And I believe that this is one of those times."
Two recent polls show Americans oppose airstrikes, with a Pew Research Center survey showing 48 percent opposed to 29 percent in favor and a Washington Post-ABC News poll showing 59 percent opposed and 36 in support. Both surveys were taken over the recent Labor Day holiday weekend as the U.S. released its assessment of whether the Syrian government used chemical weapons and Obama announced he would seek congressional approval.
Sen. Dianne Feinstein, D-Calif., chairwoman of the Senate Intelligence Committee, said the public sentiment might be different if Americans could see the evidence from the chemical weapons attack, including the convulsions and other side effects of the nerve gases.
"They don't know what I know. They haven't heard what I've heard," she said.
An Associated Press survey found 34 senators in support or leaning in favor of authorizing military action, 32 against or leaning that way and 34 undecided ahead of votes next week. Tallies in the House show a significant number of Republicans and Democrats are also opposed to military action or leaning against it.
Senate Majority Leader Harry Reid on Friday formally introduced the resolution, which would authorize the "limited and specified use" of the U.S. armed forces against Syria for 90 days while prohibiting American ground troops from combat. Lawmakers return from their five-week recess on Monday and will begin to debate, with a Senate vote to move ahead on the resolution expected Wednesday.
"I think we're going to get 60 votes. It's a work in progress," Reid said.
Obama's unexpected decision last week to seek congressional approval halted what had seemed to be a march toward quick military action in retaliation for a chemical weapons attack the U.S. says was perpetrated by Assad's government. Obama has repeatedly said the deployment of the deadly gases would cross a "red line" and change his calculus regarding a bloody civil war in which he has been reluctant to intervene.
If Congress votes down a resolution authorizing force, the president could risk further damage to his credibility if he doesn't follow through on his warnings to Assad. But moving forward against the will of Congress could worsen his already difficult relationship with Republicans and jeopardize the rest of his legislative agenda.
Earlier Friday, White House deputy national security adviser Tony Blinken said of the president that it is "neither his desire nor his intention to use that authority absent Congress backing him." Obama deflected a question about the remark during his news conference, again refusing to give a yes-or-no answer about what he would do if Congress turns him down.
On the ground in Syria Friday, a monitoring group said the government sent reinforcements, including tanks and armored personnel carriers, to a predominantly Christian village north of Damascus where rebels have battled government troops this week. Opposition fighters led by an al-Qaida-linked rebel faction had attacked the ancient mountainside sanctuary of Maaloula and briefly entered the village. The assault has spotlighted fears among Syria's religious minorities about the prominent role of Islamic extremists in the rebel ranks fighting to overthrow Assad.
Meanwhile, the Kremlin said Russia was boosting its naval presence in the Mediterranean Sea, moving warships into the area. That was stoking fears about a larger international conflict if the United States orders airstrikes.
The U.S. already has five Navy destroyers armed with Tomahawk missiles on standby in the Mediterranean.
Associated Press writers Nataliya Vasilyeva, Angela Charlton and Julie Pace in St. Petersburg, and Donna Cassata and Nedra Pickler in Washington contributed to this report.