Congress' fall slate of business, already daunting, has been made all but impossible by the looming showdown over military action in Syria.

The plan had been for Congress to avoid an Oct. 1 government shutdown and then cut a deal to raise the debt ceiling before default is threatened in mid-October. Meanwhile, the House was supposed to pick up where the Senate left off on immigration reform legislation as well as work on a farm bill. In the background was the swiftly approaching Oct. 1 opening of the Obamacare exchanges, an event some Republicans were hoping to stave off. All of this had to be resolved in just 16 legislative days in the House.

But now the votes on Syria are shaping up to be a watershed moment for the Obama administration’s foreign policy and for Congress — and an obstacle to the rest of the agenda. The president faces a tough challenge in winning authorization of military force from lawmakers who are mindful of pervasive public skepticism about an attack.

A USA Today poll found that Americans oppose military action against Syria by 63-28 percent.

Facing an anti-intervention environment on Capitol Hill, the White House launched an all-out effort to win support that promises to occupy the attention of both Congress and the public.

“Even limited wars can suck most of the oxygen out of the place,” Wilson Center congressional scholar Donald Wolfensberger told the Washington Examiner. He noted that Congress will be hard-pressed to meet just the fiscal deadlines it faces: Even if it punts on the budget issue with a short-term continuing resolution, it would still face a crunch just to raise the debt ceiling in the time left. Something will have to give: “Congress truly is already well into the fall season, and the mega question is: What is going to fall?” he said.

Stan Collender, a budget expert and partner at the public-relations firm Qorvis, predicted that the Syria debate would result in the fiscal reckoning being postponed, calling the vote over military action a “federal budget debate get-out-of-jail-free card.”

“GOP leadership now has an easy-to-explain excuse to use with its caucus to delay debating the budget over the next few weeks without having to deal with defunding Obamacare or spending cuts,” Collender wrote in a post on his budget blog. “Syria makes a short-term CR and debt ceiling increase far more likely.”

Nevertheless, the Republican leadership insists that it can clear its plate in the short September-October timeframe. “We are confident we can address a resolution on the use of force in Syria and still meet our other obligations in a fiscally responsible manner,” said Brendan Buck, a spokesman for House Speaker John Boehner.

Even in the unlikely event that Congress keeps to its planned schedule, some items that don't have a hard deadline will fall out of the spotlight entirely. Most importantly, the push for immigration reform appears to have lost all its momentum.

The Senate passed a comprehensive immigration reform bill in June, but the House had not coalesced around an approach for considering legislation before the August recess.

Advocates had hoped that lawmakers would feel pressure to move on the issue after hearing from constituents in their home districts, but Syria became the top storyline of the recess. Videos of Republican John McCain’s town hall meetings in Arizona showed voters berating him for supporting the administration’s proposed attack, not for his vote for the Senate immigration bill. On short notice, Michigan Republican Rep. Justin Amash scheduled a 30-hour, 11-stop tour around his district to address the scheduled war vote.

Rep. Raul Labrador of Idaho, a Republican influential in the House’s immigration debates, blamed Syria and the packed legislative calendar for the focus shifting away from reform, telling the Associated Press, "I don't think there's going to be sufficient time for us to discuss immigration."

If the House doesn’t act on immigration by Thanksgiving, there is likely not enough time remaining in 2013 to pass a bill. And action isn't likely in 2014 either, with lawmakers facing reelection. Immigration reform could wind up the biggest victim of an overcrowded schedule.