Larry Summers in 2010. REUTERS/Arnd Wiegmann President Obama still looks set on nominating Larry Summers to chair the Federal Reserve.

But burgeoning resistance among Democratic senators and the complication of the Syria attack make it look less clear that he can be confirmed. Here are three key problems for a Summers nomination:

1. The Senate Banking Committee must approve the Summers nomination before it goes to the full Senate, and Democrats there are resistant. According to the Wall Street Journal, congressional aides expect three Democrats on that committee to oppose summers: Elizabeth Warren (Mass.), Sherrod Brown (Ohio), and Jeff Merkley (Ore.) If three Democrats vote 'no' on Summers, he won't be able to get out of committee without Republican support.

Other Democrats on the committee are not exactly clamoring for Summers either, though the Journal reports that Chairman Tim Johnson (D-S.D.) is expected to be supportive. I reached out to the offices of the remaining Democrats on the committee to ask if they are open to voting for Summers. Only one responded favorably; the rest were noncommittal:

Chuck Schumer (N.Y.) thinks both Summers and Yellen would be "very good choices," according to spokesman Matt House.

Jack Reed (R.I.) " will consider any person the President chooses to nominate," per spokesman Chip Unruh.

Heidi Heitkamp (N.D.) " is closely examining all individuals who have been mentioned as potential candidates," according to a spokesperson.

Robert Menendez (N.J.): No comment.

Mark Warner (Va.): No comment.

Spokespeople for Kay Hagan (N.C.) and Jon Tester (Mont.) did not respond to requests for comment.

2. President Obama is already asking liberals for a big favor by seeking their support for an authorization to attack Syria. Many Democrats in Congress are instinctively opposed to military action. They also remember the price Hillary Clinton paid for voting for a war that voters came to regret. If Obama nominates Summers, he'll be coming back to those same liberals just weeks later and asking them to defy their base again.

Nineteen Senate Democrats and independent Angus King (Maine) have reportedly signed a letter urging Obama to nominate Fed Vice Chair Janet Yellen, the implication being that he should not nominate Summers. Liberals have a variety of concerns about Summers, relating to monetary policy, bank regulation, his views on women, and his temperament. (Some conservatives share some of these concerns, too.)

Whether or not the Syria resolution passes, it uses up some of the political capital Obama was supposed to be saving to buy support for Summers from the left.

3. If the Syria resolution fails, the President will be unable to afford another defeat in Congress. There's no way for him to avoid bitter fights over raising the debt ceiling and passing a funding bill to keep the government open for another year. Picking a fight over Summers is optional.

My guess: If the Syria resolution gets approved, Obama will go for Summers. If it's defeated, Obama will punt where he can by picking an uncontroversial Fed nominee. The key question is whether that means Yellen or someone else who might not be as committed to accommodative monetary policy.