But members of Congress clearly see recent events creating an opening in the postelection session of Congress, when some retiring and defeated lawmakers could have a freer hand on voting for legislation, absent political consequences. Republicans were weakened by losing seats in both the House and the Senate, while Democrats are eager to move to issues like immigration, which animated Latino voters and helped deliver victory on Tuesday. “The conditions are there to act,” Mr. Corker said. “I think the environment is different now.”

Even conservative Republicans are signaling newfound flexibility. Aides said that on a conference call of House Republicans, a number of lawmakers spoke up to say they needed to give their leaders breathing room and avoid brinkmanship.

The budget office report suggested that allowing the Bush-era tax cuts to expire for households earning more than $250,000 a year — a position strenuously opposed by Congressional Republicans — would have relatively modest economic impacts, versus many of the other components of the fiscal cliff.

“House Republicans must end their intransigence on tax cuts for the very wealthy and sit down on a bipartisan basis to finish the work of this Congress,” said Representative Sander M. Levin of Michigan, the ranking Democrat on the House Ways and Means Committee.

A separate C.B.O. report released Thursday threw cold water on Republican beliefs that a simplified tax code that lowered income and payroll taxes and closed loopholes to make up for lost revenue would substantially close the deficit by boosting economic growth. Such a plan would raise about $100 billion a year by 2020, far less than Democrats say is necessary, the report said.

The forces arrayed against a budget deal remain powerful, and the gap between the parties — at least in their public postures — is wide. Liberals, backed by Senator Harry Reid of Nevada, the majority leader, say Social Security should not be part of any deal. Senator Bernie Sanders, independent of Vermont and a standard-bearer for the left, said Thursday that virtually all deficit reduction should come from tax increases on the rich, closing loopholes that have allowed profitable corporations to avoid paying any corporate income taxes and cutting military spending.