December was supposed to be a sleepy month for Congress — a chance to finish up a productive lame-duck session and leave the decks clear for the new Republican majority that takes control in January.

Instead, the next two weeks have morphed into a minefield. Government funding is suddenly in peril, as conservatives fume over President Barack Obama’s decision to end the deportation threat for millions of undocumented immigrants. Republicans and Democrats and the White House are locked in battle over extending lapsed tax provisions popular with corporate America. Congress had already punted a few issues into the new year, such as a broader debate about the president’s war powers and voting on important executive-branch nominees.

As Congress returns from its Thanksgiving break, problems are plentiful and finding solutions will test leaders of both parties — particularly Republicans, whose moves now could determine whether they can change the tone on Capitol Hill and prove the days of governing by crisis are over.

First up: funding the government. The government will shut down Dec. 11 unless a funding bill is passed, and Speaker John Boehner of Ohio — the most powerful Republican in power until January — has to quell the furor within the House Republican Conference over Obama’s immigration order to avoid an unwanted and dangerous December showdown.

The politics are delicate for Boehner, House Majority Leader Kevin McCarthy (R-Calif.) and Majority Whip Steve Scalise (R-La.). A healthy number of House Republicans believe Obama overstepped his executive authority when he stopped deportations for millions of undocumented immigrants, and many of those lawmakers want to use the upcoming government-funding debate to hold his feet to the fire.

But inside Republican leadership, senior aides and lawmakers freely admit that the executive order — no matter how unpopular it is — will likely stand and there’s little Congress can do about it. So Boehner, McCarthy and Scalise need to craft a process that will allow conservatives to vent, but prevent a shutdown.

The strategy will begin to take shape Tuesday morning, when the GOP meets in a closed session in the Capitol basement.

One scheme has emerged as a favorite. The leadership would like to craft two bills to fund the government: one that would keep most of the government open through September 2015, and another that would fund immigration enforcement agencies through the first few months of the year. There’s also the potential for stand-alone legislation to try to target Obama’s executive action.

GOP hard-liners have ideas of their own. Some have floated censuring Obama or canceling his State of the Union address, although neither will happen, senior aides say. Legislation is unlikely to come to the floor until next week.

This isn’t exactly how Boehner and McCarthy envisioned this lame-duck session of Congress. House Appropriations Chairman Hal Rogers (R-Ky.) has been working for months to craft a large-scale omnibus spending bill that would remove the threat of a shutdown until late into 2015. Republicans envisioned a productive first quarter of 2015, but now they are suddenly facing another funding fight in February or March.

For Boehner, the politics are particularly dicey. On Jan. 3, he will stand for reelection as speaker. If he loses any more than 26 GOP votes, he’ll lose the speakership. There is no immediate threat to his power, but Boehner must move cautiously during this upcoming session in order to limit conservative opposition to his speakership.

Boehner and outgoing Senate Majority Leader Harry Reid (D-Nev.) also find themselves in an unexpected fight over the tax extenders package.

The White House threatened to veto the $450 billion agreement between Reid and Boehner because it did not cover expansions of the child tax credit and earned income tax credit favored by Obama. The package would also add hundreds of billions of dollars to the deficit over the next decade.

Reid backed the bipartisan package because it would extend the deduction for state sales taxes, which is important in his home state of Nevada, which has no income tax.

The veto threat has left the fate of the tax extenders package up in the air, and it’s not clear that it will get done during the lame-duck session.

The White House’s move also laid bare the growing rift among Democrats since their humiliating Election Day defeat, which robbed them of control of the Senate majority. There’s an ongoing struggle going on within the party over why Democrats lost so badly on Nov. 4, a fight that will continue to play out during the lame-duck session.

Some progressive Democrats are calling for Obama and Democratic leadership to adopt a more aggressive populist economic message. Moderate Democrats, however, want to see the party move more mainstream, to appeal more directly to middle-class voters. In a speech last week, New York Democratic Sen. Chuck Schumer said Democrats focused too much on passing health care reform — Obamacare — when they controlled the White House and Congress in 2009 and 2010. “The focus on Obamacare gave anti-government forces and the Republican Party new vigor and new life, at least temporarily” and led to GOP victories in 2010, he said.

Schumer’s comments touched off a furor on the left, and the message was repudiated publicly by some senior former Obama administration officials.

Schumer also quietly announced on Friday that he’s adding Sen. Mark Warner of Virginia, a moderate, to the Democratic communications and policy team, seeking to balance the more populist Sen. Elizabeth Warren of Massachusetts.

“Mark is a natural leader in our caucus who will bring a diverse experience of both private sector and public service work to this new role,” Schumer said in a statement. “In the next Congress, Mark will work closely with the entire DPCC team to put forward policies and a message that resonate strongly with America’s middle class.”