What Congress is and isn't likely to do in the lame duck session

Lawmakers return to Washington after Thanksgiving break with a long agenda and just weeks until a new Congress begins.

Come Jan. 3, Republicans will run the House, ending two years of total Democratic control of the federal government. Already, GOP members are jockeying for new leadership positions and turning their attention toward how they will mount a response to the Biden agenda.

But partisan preparation aside, the next few weeks are going to require some across the aisle cooperation if Congress is to get anything done in what is known as the lame duck between the election and the end of the current term. There is a laundry list of must-pass agenda items hanging in the balance. Among them: funding the government and passing a massive military spending bill.

Democrats, meanwhile, will look to maximize their final days unchecked by GOP blockades.

Dems zero-in on 2 outstanding priorities

Democrats are expected to seal a win later this week by finally passing federal legislation that would enshrine into law protections for same-sex and interracial marriages. While procedural votes still remain, the legislation cleared a key test vote in the Senate just before Thanksgiving, with 12 Republicans joining all Democrats in the chamber to prevent a filibuster.

"Let me be clear: Passing the Respect for Marriage Act is not a matter of 'if' but only of 'when,'" Majority Leader Chuck Schumer said after that successful vote.

Approving the legislation would be a victory for Democrats who have been seeking to codify same-sex marriage -- currently legalized by the Supreme Court decision Obergefell v. Hodges -- since the high court overturned the right to an abortion earlier this year, with Justice Clarence Thomas suggesting in a separate opinion that Obergefell should also be reversed.

While the Senate's marriage bill will need to return to the House once passed, a previous version cleared the House with the support of 47 Republicans.

Democrats also hope to take up legislation later this month that aims to clarify the role, as spelled out in the Electoral Count Act (ECA) of 1887, that the vice president plays in certifying election results. The new legislation is intended to head off arguments like those made by former President Donald Trump around Jan. 6, 2021: that the vice president holds the power to unilaterally reject electors presented by the states. The legislation would instead define the vice president's role in certification as purely ceremonial.

ECA reform comes after months of behind-the-scenes bipartisan coalition building and has more than the requisite 10 Senate Republican co-sponsors, including Minority Leader Mitch McConnell. But it's still not clear if or when the Senate will take it up.

"We're working on it. We want to get it done," Schumer said Monday when asked about the timing of a potential vote.

Other priorities are likely to fall on the cutting room floor as the clock ticks down.

Some Democrats had hoped to pass some sort of immigration reform to secure a pathway to citizenship for recipients of the Deferred Action for Childhood Arrivals, whose fate currently awaits a court ruling. But there's little appetite for such a measure from Republicans and at least 10 would be needed to move any proposal in the limited remaining time.

A group of Democrats are also angling to reinstate their popular, pandemic-era child tax credit. Success on that front is also unlikely.

Any legislation that fails to make it to the finish line come the installment of the new Congress, in January, must return to square one with the next group of lawmakers.

Leadership fights take center stage

While Democrats will look to make the most of their remaining weeks in control of both chambers of Congress, House Republicans will spend much of that time trying to figure out who will be at the helm come Jan. 3.

Current House Republican leader Kevin McCarthy is eying the speaker's gavel, but it remains to be seen if he'll have the votes he needs to secure it. Earlier this month, he won his party's nomination during a closed-door election. But it was far from unanimous support among his own party -- which will control at most 222 seats in the next House -- and to clench the speakership, McCarthy will need 218 votes, which means he can avoid few defections.

So far, five House Republicans have said they are hard "no" votes for McCarthy.

Meanwhile, House Democrats will elect a new, history-making generation of leaders this week during elections on Wednesday and Thursday, following Speaker Nancy Pelosi's pre-Thanksgiving announcement of her intention to step away from party leadership.

Rep. Hakeem Jeffries of New York is largely expected to ascend to Pelosi's post. Jeffries won't have to scrap for votes; he is expected to take over for Pelosi with the overwhelming -- if not unanimous -- support of his caucus, putting the 52-year-old on track to be the first Black lawmaker to lead a party in Congress.

It will also be the first time in 20 years that Pelosi hasn't been in that role. The whip will be a woman -- Katherine Clark of Massachusetts -- and the No. 3, Pete Aguilar, will become the highest-ranking Latino in Congress; the Californian rose to prominence from his perch on the high-profile Jan. 6 committee.

Republican leadership in the Senate has already been decided, with members meeting behind closed doors last week and overwhelmingly selecting McConnell to remain at the party helm, despite facing his first challenge for the position in 15 years.

Rick Scott of Florida, the outgoing head of Senate Republicans' campaign arm, had 10 supporters back his bid to replace McConnell.

Senate Democrats are expected to hold their leadership elections later this month, likely after the Dec. 6 Georgia runoff election. Schumer is largely expected to remain atop the party.

Lawmakers will grapple with must-pass funding

One thing lawmakers must do in the coming weeks of the lame-duck session is fund the government. Current funding runs out on Dec. 16.

Democrats want to try to pass a year-long funding package composed of 12 major bills rolled into one. But there's yet to be an agreement on a top-line figure for that massive package, slowing negotiations.

A huge sticking point in those discussions has been a request from the Biden administration to provide Ukraine with $38 billion in additional funding -- the latest in a series of such aid -- to assist the country in its war against Russia.

All along, funding for Ukraine has had strong bipartisan support. But some Republicans have recently signaled that the party would not back additional funding during the lame-duck without guarantees of what they called transparency and accountability.

McCarthy has said his conference would not support writing a "blank check" for Ukraine if they captured the majority. He later walked back his comments, saying he is supportive of Ukraine. Reps. Michael McCaul and Mike Turner said on "This Week" on Sunday that the incoming House Republican majority will support Ukraine, downplaying critics inside the GOP like Rep. Marjorie Taylor Greene.

There are a few paths forward to avert an immediate shutdown. Among them is a short-term funding bill to punt the problem slightly down the road, giving lawmakers more time to make a deal. Some Republicans favor this option, figuring they'll have more negotiation power in the House come Jan. 3.

It's not yet clear how Congress will maneuver through this and, before they do, senators are also set to wrangle a must-pass military appropriations bill: the National Defense Authorization Act.

That must-pass legislation has cleared the chamber every year for 50 years, and this Congress is behind schedule.

Chance to raise debt limit seems to be slipping

The federal debt limit, which allows the government to borrow money in order to pay for spending required by Congress, will need to be raised sometime next year. But previous increases of the debt limit -- as under President Barack Obama and a Republican Congress -- became politically poisonous battles.

Some Democrats in this Congress want to go ahead and deal with it now, before GOP cooperation is required in the new year.

Some House Republicans, meanwhile, have indicated they will use a deal over raising the debt limit to extract cuts to government spending, such as on social programs.

But hiking the limit without GOP support would require use of a cumbersome fast-track budget process known as reconciliation. The process eats up an incredible amount of floor time, all but wiping Democrats' chances of using their remaining weeks in control to tackle other priorities.

While Democratic leadership has signaled interest in raising the debt limit before turning the House gavel over to Republicans, it does not seem likely to happen this Congress.

ABC News' Lauren Peller contributed to this report.