A mashup of President Obama's answers to questions asked Friday about Syria at a news conference in St. Petersburg. (The Washington Post)

There was a moment Friday when the leader of the free world explained the awe and sympathy his job provokes among colleagues.

At the end of a Group of 20 summit in Russia, President Obama recounted a recent conversation he had had with another head of state, as the question of whether the United States would soon attack Syria loomed over the gathering.

“I’m a small country, and nobody expects me to do anything about chemical weapons around the world,” Obama quoted his fellow leader as saying. “They know I have no capacity to do something, and it’s tough because people do look to the United States.”

Then, shifting to his own voice, Obama said: “And the question for the American people is, ‘Is that a responsibility that we’re willing to bear?’ ”

At the heart of Obama’s parable about the burdens of power is the reason why a second-term president has suddenly turned to an unpredictable, unruly and often-hostile Congress for a decision on war.

He wants an answer to his question: What, after nearly a dozen years of war, is the country willing to bear? Obama appears willing, so far, to risk a severe setback to his presidential prestige to get an answer, even if it turns out to be — as seems quite possible — that the country will not support even a limited military intervention in Syria’s civil war.

His decision to seek congressional approval to attack Syria, where 120,000 people have been killed since Obama first called for President Bashar al-Assad to step down, baffled even his closest advisers. Obama made the decision on his own, less than two weeks after Assad allegedly used poison gas to kill 1,500 people, hundreds of them children.

Now Obama is demanding that Congress — and, by extension, the U.S. electorate — clarify where, when and why the United States should act militarily — not just in Syria, but also in the next region roiled by atrocity.

As early as next week, Congress will vote whether to allow Obama to begin limited military strikes against Assad’s government, which may have first crossed Obama’s stated “red line” of chemical weapons use late last year in an attack the administration still considers under investigation.

Consistent with polls showing scant support for a Syrian operation, the “no” votes have been piling up, especially in the House. As of Friday, more than half of the House, including dozens of Democrats, have declared themselves against or leaning against such a resolution, according to a Washington Post analysis.

Securing a resolution appears remote as Obama returns to Washington. Strong resistance is coming from inside his own party — the one that nominated him in 2008 because of his clear stance against the Iraq war — and on Tuesday he intends to speak on Syria from the White House to a national audience.

A new military operation would run counter to the overall direction of the administration, which has been focused on ending two long U.S. wars in Iraq and Afghanistan. As one senior administration official said about Afghanistan this year: “In the background of everything we will do this term is ending the war, however you want to define it.”

Now it is an anti­war political argument, made loudest by fellow Democrats, that Obama is seeking to counter.

He is doing so with a warning about the precedent set by Assad’s alleged violation of international norms, the essential horror of those dying in Syria, and an appeal for political courage beyond polling — a rule he has not always lived up to himself.

“It’s conceivable that at the end of the day, I don’t persuade a majority of the American people that it’s the right thing to do,” Obama said. “And then each member of Congress is going to have to decide, ‘If I think it’s the right thing to do for America’s national security and the world’s national security, then how do I vote?’ ”

His own military venture in Libya two years ago, which ended with Moammar Gaddafi’s death, was celebrated as a model at the time for the way the United States could help organize an operation, participate in its decisive first stage and then turn over command to allies.

Obama did not seek congressional approval for the operation, which he argued was necessary to protect the people of Benghazi from Gaddafi’s threats of a city­wide massacre. He did, however, win U.N. Security Council and Arab League approval for military action — neither of which he has been able to accomplish this time. His appeal will be to Congress.

“Those kinds of interventions, these kinds of actions are always unpopular, because they seem distant and removed,” Obama said Friday.

“When people say that it is a terrible stain on all of us that hundreds of thousands of people were slaughtered in Rwanda, well imagine if Rwanda was going on right now,” he said. “And we asked: ‘Should we intervene in Rwanda?’ I think it’s fair to say that it probably wouldn’t poll real well.”

Obama has often contrasted his multi­lateral approach to the more go-it-alone propensity of the George W. Bush administration — an attribute the Nobel Peace Prize committee highlighted in giving Obama the award in 2009.

But on Friday, Obama echoed the frustrations of his predecessor over the United Nations,

saying the Security Council was suffering “paralysis” on the Syria issue.

“There are going to be times, though, where, as is true here, the international community is stuck for a whole variety of political reasons,” he said. “And if that’s the case, people are going to look to the United States and say, ‘What are you going to do about it?’ And that’s not a responsibility that we always enjoy.”