The first matter to be settled is how much money the government should spend overall in 2018. The pre-Christmas deadline is aimed at forcing Republicans and Democrats to agree on a top-line budget number, which would then apply to an omnibus appropriations bill that Congress would pass in January. Trump is demanding another big increase in defense spending, on top of the $15 billion boost he secured in the spring. But Democrats say they’ll only go along with that request if Congress approves an equal bump for domestic agencies—a change that would reverse the steep reductions called for in the Trump administration’s budget proposal.

Far more contentious are the debates about extraneous bills that Democrats and some Republicans are insisting on attaching either to the next government funding bill later this month or to the much bigger spending bill in January. Immigration tops that list. “We will not leave here without a DACA fix,” Pelosi vowed on Thursday before the White House meeting. She was referring to legislation offering permanent legal status—and potentially citizenship—to immigrants who were protected from deportation under former President Barack Obama’s Deferred Action for Childhood Arrivals program.

Trump has said the program will end in March unless Congress acts, and Democrats want the legislation included in exchange for their votes for a spending deal. Several dozen House Republicans have joined their call, but GOP leaders in both chambers are bowing to conservative opposition to tying the two issues together. “While all agreed on the need to address the DACA population, the Republican leaders stressed the need to address border security, interior enforcement, and other parts of our broken immigration system and that this should be a separate process and not used to hold hostage funding for our men and women in uniform,” spokesmen for House Speaker Paul Ryan and Senate Majority Leader Mitch McConnell said in a joint statement after meeting with Trump and the Democratic leaders.

Instead, Republicans say they’ll address DACA early in 2018 as part of a broader package tightening border security and cracking down on illegal immigration. But DACA alone could cause a government shutdown if Democrats hold the line. “They would be doing exactly what we did with Obamacare in 2013,” warned Representative Tom Cole of Oklahoma, a senior House Republican. “They’re free to do it. They have the votes to do it, particularly in the Senate. But I think in the end it actually drives Republicans together.”

Health care is even more complicated. In exchange for her support of the Republican tax bill, Senator Susan Collins of Maine extracted a commitment from party leaders that two bipartisan proposals to shore up the Affordable Care Act’s insurance markets would pass by the end of the year, likely as part of the spending deal. Collins said those bills—one to restore payments to insurers that Trump cancelled and another to fund reinsurance programs—would mitigate the impact of repealing the law’s individual mandate in the tax bill. But conservatives in the House want no part of Collins’ deal. “I think that would be a full-scale revolt on our side,” Cole told me.