What if Congress votes no on Syria?
President Obama's heading back to the US for a horrible week ahead. He spoke at at news conference in Russia like a man who felt agonised by his own choice.
He said: "I'm not itching for military action". He added: "I've spent the last four-and-a-half years doing everything I can to reduce our reliance on military power as a means of meeting our international obligations and protecting the American people."
To some, watching him wrestling with difficult issues will make him a more authentic proponent of a tough choice. But it may not be the best frame of mind for a man who has to sell a plan like his whole reputation rests on it.
"This is not convenient. This is not something that I think a lot of folks around the world find an appetising set of choices," he said.
"But the question is, do these norms mean something? And if we're not acting, what does that say?"
He added that the leader of a small country said he was glad nobody looked to his country to take action. But people did, the president said, have that expectation of America.
"It's tough because people do look to the United States. And the question for the American people is, is that a responsibility that we're willing to bear?
"And I believe that when you have a limited, proportional strike like this - not Iraq; not putting boots on the ground; not some long, drawn-out affair; not without any risks, but with manageable risks - that we should be willing to bear that responsibility."
Intriguingly, he suggested he went to Congress because he knew he didn't really have the authority under the law to take action, in this case, without it.
"I put it before Congress because I could not honestly claim that the threat posed by Assad's use of chemical weapons on innocent civilians and women and children posed an imminent, direct threat to the United States," he said.
But he refused to say what he would do if Congress voted "no". That, he said, would be jumping the gun.
But all the indications from Congress are that the "no" votes are piling up. If there is one, that will present the president with his next agonising choice.