Congress will return to Washington this week to confront a series of highly charged partisan issues as a deadline for extending government funding approaches, raising the specter of a December government shutdown.

Leaders of both parties have publicly played down the possibility of a showdown next month. Funding expires on Dec. 8, and both sides have floated the possibility of a short-term stopgap to push negotiations until just before Christmas.

“There shouldn’t be any discussion about shutting down the government. We can make this thing work. We just need to get people at the table, negotiate it,” Sen. John Thune (S.D.), the third-ranking Republican senator, said on “Fox News Sunday.”

But informal talks have been abortive, and bitter partisan divides over spending, health care and immigration threaten to set up an impasse.

The tone could be set quickly. Congressional leaders of both parties are set to meet Tuesday with President Trump at the White House in a summit that could smooth the path for the month ahead — or inflame simmering fights.

President Trump meets with Senate Majority Leader Mitch McConnell R-Ky.) and House Speaker Paul D. Ryan R-Wis.) at the White House in March. Democratic leaders will join the three for a summit Tuesday. (Bill O'Leary/The Washington Post)

The last time Trump met with those top leaders — House Speaker Paul D. Ryan (R-Wis.), Senate Majority Leader Mitch McConnell (R-Ky.), House Minority Leader Nancy Pelosi (D-Calif.) and Senate Minority Leader Charles E. Schumer (D-N.Y.) — he sided with the Democrats ahead of a September deadline, averting a standoff over spending and the federal debt limit.

Trump has not indicated whether this time he will be as amenable. Multiple aides in both parties cautioned that the meeting might not yield an agreement — partly because key issues bedeviling the leaders remain unresolved and also because Republicans want to keep the focus this week on their sweeping tax bill.

While Republicans try to wrap up their tax effort, they must negotiate with Democrats on the litany of other governing items. The first step toward a resolution will be reaching an agreement on government spending levels for 2018 and perhaps beyond, lifting caps imposed under a bipartisan 2011 budget deal.

“I just say, be ready for a potentially wild month in December,” said Rep. Charlie Dent (R-Pa.), a senior member of the House Appropriations Committee who for months has pushed GOP leaders to reach a spending accord with Democrats. “This is going to get a bit complicated.”

Under current law, Congress may appropriate no more than $549 billion for defense programs and $516 billion for nondefense programs next year, a cut from current levels.

But the Trump administration and defense hawks want to boost defense spending to more than $600 billion, and Democrats are demanding a dollar-for-dollar increase in nondefense spending. Because House Republicans have needed Democrats to help pass spending bills in recent years amid opposition from fiscal conservatives and because Senate Democrats can filibuster any spending bill, party leaders have leverage to force a deal.

“We’re going to need their help,” Dent said of Democrats. “And the question for the Democrats is: Are they going to play ball with us?”

Talks before the Thanksgiving holiday focused on raising spending levels somewhere between $180 billion and $200 billion over the next two fiscal years combined but went nowhere, according to multiple people familiar with the negotiations. Aides from both parties warned that if a spending accord is not reached this week, hopes for the passage of a broad appropriations bill before Christmas would be dim.

The GOP tax bill, which is being considered under special procedures that do not require bipartisan cooperation, has made some Democrats increasingly resistant to collaborating with Republicans in any sense.

“The decisions made during the next month will affect Americans’ economic well-being for the next decade,” Sen. Amy Klobuchar (D-Minn.) said Sunday. “Our job is to break through all the tweets and the noise and focus on the economics at hand.”

Aside from the basic task of keeping the government open, lawmakers also are pushing to deliver tens of billions of dollars in additional federal aid to disaster victims across the country before the year ends, including those affected by hurricanes Harvey, Irma and Maria, as well as by Western wildfires. The White House requested another $44 billion in aid this month and asked that the increased spending be offset by unrelated spending cuts, a proposal that quickly earned bipartisan criticism.

Complicating the passage of any spending deal are the highly charged politics of health care and immigration.

Democrats have pushed for the passage of bipartisan legislation drafted in the Senate that would help stabilize the market for individual insurance coverage established under the 2009 Affordable Care Act by appropriating funds that allow insurers to reduce out-of-pocket costs for low-income Americans. Trump canceled the payments, which had previously been made absent congressional appropriation, in October.

But conservative Republicans have opposed any attempt to shore up the ACA, and the GOP tax bill could eliminate a core provision of the law: the tax penalty meant to compel Americans to secure insurance coverage. Moderate Republican senators Susan Collins (Maine) and Lisa Murkowski (Alaska) have said they would like to see the stabilization bill pass alongside any repeal of the ACA mandate, but Schumer has said Democrats would not support passing the stabilization bill under those circumstances.

In a declaration that could put Democrats on edge, Trump said in a Thanksgiving Day tweet that he would continue pushing to repeal the law entirely in the new year: "Even though the Dems want to Obstruct, we will Repeal & Replace right after Tax Cuts!"

Immigration could be an even more emotionally charged issue for Democrats. Dozens of liberal lawmakers have vowed to withhold their votes for any spending bill if Trump and Republicans refuse to use the must-pass legislation up for consideration this month as a way to provide legal protections to hundreds of thousands of “dreamers,” the young children of undocumented immigrants.

Trump announced the end of the Deferred Action for Childhood Arrivals program in September, giving Congress until March to codify protections for the young immigrants the program protects or risk their eventual deportation. Given the leverage Democrats have in the House and Senate, some of their most liberal members — including Sen. Kamala D. Harris (D-Calif.) and Rep. Luis V. Gutiérrez (D-Ill.) — are calling on Schumer and Pelosi to force the issue this month in talks with Trump, McConnell and Ryan.

Trump, meanwhile, continues to push for funding for a Mexican border wall — a request Democratic leaders have so far rejected outright. It remains on the administration’s wish list for a year-end spending deal.

While dozens of Republican lawmakers have joined Democrats in calling for a resolution to the “dreamer” issue, senior GOP aides continue to dismiss the idea that an immigration agreement can be included alongside complex fiscal concerns.

“There is no immediate deadline for DACA,” one senior Republican aide said, dismissing Democrats’ vows to withhold support. Another senior aide called the push for a resolution this month “nonsense,” given the March deadline.

Ryan told reporters earlier this month that he wants to complete a 2018 spending bill before lawmakers break for Christmas. But a key conservative leader said Sunday that he considered such a schedule “highly unlikely,” given the amount of unfinished business on the GOP agenda.

Rep. Mark Meadows (R-N.C.), chairman of the House Freedom Caucus, suggested that a stopgap should instead extend spending talks into January. That would give Republicans time to complete the tax bill and focus on preserving GOP priorities in any deal with Democrats.

“To suggest that the Democrats are driving the narrative under a Republican administration and can demand whatever they want for an end-of-the-year spending bill would beg the question: What’s different from this administration to prior administrations?” he said. “It would be very problematic for most of the voters that turned out to vote for a change” in last year’s presidential election.

Looming over everything is the Dec. 12 special election in Alabama, which could narrow the already tight Republican majority in the Senate. Republican nominee Roy Moore, running to fill the seat vacated by Attorney General Jeff Sessions, has been fighting allegations of sexual misconduct. Democratic nominee Doug Jones leads in some polls.

A Jones victory could spell doom for the GOP tax bill if it is not passed into law by the time he would be seated, probably in late December or early January. A Moore victory would carry its own risks, given his enmity for McConnell and GOP establishment leaders.

“If Roy Moore wins and he comes into the Senate in January, there’s going to immediately be an ethics investigation, which is going to be a cloud . . . and is going to be a distraction for us and our agenda,” Thune said Sunday.

Besides the spending battle, other major deadlines are approaching.

The Children's Health Insurance Program expired Sept. 30, and Congress has yet to come to a bipartisan agreement to reauthorize it, leaving health coverage for nearly 9 million in limbo. While states have been able to continue their programs using surplus funds, at least five states say they will inform families that their coverage is in jeopardy and begin winding down their programs if Congress does not act in coming weeks.

A federal law that allows intelligence agencies to gather foreign electronic communications on U.S. soil will expire Dec. 31, potentially taking away what the National Security Agency has called "the single most important operational statute" at its disposal unless Congress acts to renew it. Several lawmakers want to constrain the government's authority to search intelligence gathered under the program for information about Americans. While there are bipartisan bills to revise and extend the law, no agreement has been reached to advance them.

Congress also is under pressure to decide whether it wishes to reimpose sanctions on Iran that were lifted as part of the 2015 nuclear deal, following Trump's October declaration that Tehran was not in compliance with the pact's terms.

The 60-day window for Congress to decide expires in December, but leading Republican senators have already indicated a preference to maintain the deal while passing new legislation to keep Iran from developing a nuclear weapon once the deal expires. That still sets up a potential January deadline for action on Iran, as Trump must continue to waive certain sanctions at that point to keep the nuclear pact intact.

Damian Paletta and Karoun Demirjian contributed to this report.