A showdown in Washington over government spending kicked off Wednesday with a high-level gathering between congressional leaders and the White House that previewed the broader fight likely to consume Washington for much of January.

The meeting between the four highest-ranking members of Congress and White House budget director Mick Mulvaney marked the initial round in an effort by Democrats and Republicans to make sure their top priorities are funded.

Multiple lawmakers characterized Wednesday's hour-long meeting in the office of House Speaker Paul D. Ryan as a positive start to negotiations, while noting the parties still have disagreements on major issues.

Emboldened by the passage of a landmark tax law, Republicans and the White House are demanding a bump in military spending and funding for President Trump's promised wall on the Mexican border. Democrats — empowered because the GOP needs them to pass any spending bill — want protections for undocumented immigrants brought to the United States as children and to keep funding in place for social programs.

Unlike the tax law, which was designed to pass with a simple majority, the spending bill requires 60 votes in the Senate, meaning the GOP would need at least nine Democrats. But after a year of partisan acrimony and a tax bill that did not garner a single Democratic vote, negotiators on both sides face challenges to reach a bipartisan accord.

If Congress can't strike a deal before Jan. 19, the government would shut down, discontinuing all services not deemed essential, freezing research initiatives, closing National Park facilities and sending home nearly half of the massive federal workforce.

Lawmakers on Wednesday expressed optimism about the start of negotiations. Sen. John Cornyn (R-Tex.), the chamber's second-ranking Republican, said Senate Majority Leader Mitch McConnell (R-Ky.) described the earlier bipartisan leadership meeting as "surprisingly good."

Cornyn is involved in the immigration negotiations and said he and other Republicans on the Judiciary Committee are meeting with Trump on Thursday to discuss the issue.

"As soon as the president will tell us, 'Okay this is something I can support,' then that gives us I think a lot of room to go talk to Democrats and say, 'Okay this is what our parameters are,'" Cornyn said.

Congress has cobbled together six short-term spending deals since Trump took office, staving off a shutdown and forestalling decisions on the larger budget and immigration questions. This time around, however, both parties face pressure to score policy concessions before agreeing to a funding extension.

The biggest push from Democrats, though, is a demand that the spending bill address the status of hundreds of thousands of young immigrants brought illegally to the country as children.

These immigrants were granted temporary protections under the Obama administration, but Trump has said he will end the program in March if Congress doesn't come up with a solution first.

GOP leaders want talks about the Deferred Action for Childhood Arrivals program, or DACA, to proceed separately from the spending talks. Democrats insist all the issues must be dealt with together, as the spending bill represents a rare moment of leverage for a party in the minority in both the House and Senate.

"I don't doubt we can reach an agreement on DACA that's acceptable to both sides," Senate Minority Leader Charles E. Schumer (D-N.Y.) said Wednesday.

White House press secretary Sarah Huckabee Sanders said Wednesday the White House was open to reaching a DACA deal this month if Democrats agreed to fund construction of a wall along the Mexico border, end a visa-lottery system and terminate a program that allows ­family-based immigration.

Democrats do not appear willing to do any of those things. Schumer said Democrats would approve more money for "border security" but called construction of a wall "absurdly expensive" and "ineffective."

Trump has threatened to veto spending bills if they failed to include some funding to begin construction of a border wall. And Republicans also face pressure to secure new funding for the military — GOP leaders want to bump up the military budget by roughly 10 percent.

"It also remains important that members of Congress do not hold funding for our troops hostage for immigration policy," Republican leaders said in a joint statement from the White House and the offices of Ryan and McConnell. "We've been clear about these budget priorities from the beginning and hope that further discussions will lead to an agreement soon."

Lawmakers are also working on disaster relief for areas ravaged by hurricanes last year. The House passed an $81 billion funding bill in December, but the Senate didn't act on it. Instead, it punted that issue onto the pile of other urgent matters now confronting Congress.

"We keep getting the can kicked down the road. We need to get that addressed, and so that's why I'm still hoping for January 19, but obviously there are a lot of moving parts," said Cornyn, who is also involved in the disaster relief negotiations.

Democrats want any increase in military funding to be matched with more money for other domestic programs, such as housing and education. And they are calling for more spending to combat the opioid crisis, veteran programs, and to shore up pension funds.

Congressional aides from both parties say political dynamics have changed since the tax law passed in December and it is unclear how either the White House or Democrats will handle the current negotiations.

Still, despite failing to stop the tax law, Democrats say they are better positioned to thwart Trump's agenda and are emboldened after picking up a Senate seat in Alabama. Sen. Doug Jones (D) was sworn in Wednesday after an upset of Republican Roy Moore in December.