WASHINGTON — Although lawmakers managed to avert a government shutdown before skipping town for the holidays, they will face a mess when they return in January.

Before the Christmas break, the House hastily unveiled and passed a stop-gap continuing resolution that keeps the government funded through Jan. 19. But, fresh from a successful, full-bore effort on tax reform, GOP leaders punted on a host of issues.

Any or all of the following issues have the potential to roil Congress in the coming weeks. It’s a situation that has the potential to derail a months-overdue agreement to fund the federal government for 2018 or add fuel for a spending deal that’s massive and all-encompassing.

Budget caps. A bipartisan agreement to increase statutory budget caps stalled as the GOP drafted and pushed through its tax overhaul. That means lawmakers have yet to cement 2018 funding for the Pentagon, where leaders warn of a readiness crisis caused by budget caps and funding instability.

Senate Majority Leader Mitch McConnell said at his year-end news conference that he’s rejecting Democrats’ insistence on parity for defense and nondefense increases to bargain for more for defense.

“Defense has been hit harder by the Budget Control Act than domestic programs,” said McConnell, R-Ky., arguing the 2013 sequester disproportionately hurt the defense budget.

House GOP defense hawks who abandoned plans to wed a full-year defense spending bill to the last continuing resolution say they have placed their faith in House Speaker Paul Ryan, R-Wis., who they expect will prevail in budget negotiations and get the Pentagon what it needs.

“The Senate would not vote for it,” House Armed Services Committee Ranking Member, Rep. Adam Smith, D-Wash.,“ said of the CR-defense hybrid. “And then the defense people on this side caved and accepted a CR they said they wouldn’t accept.”

Smith said Democrats voted in large numbers against the last CR because, “We want appropriations bills. [Republican lawmakers] cut taxes and they don’t fund the rest of the government. A CR is no way to run the Pentagon, it’s no way to run the government.”

Because the Senate returns Jan. 3 and the House returns Jan. 8, there will be precious little time to negotiate a budget deal. And even if one is quickly reached, it means appropriators will likely need another continuing resolution through the end of January to make time to flesh out 2018 spending plans to adhere to any new top lines.

FISA. Lawmakers are divided over whether to pass a clean reauthorization of the Foreign Intelligence Surveillance Act’s Section 702, a powerful government authority to conduct foreign surveillance on U.S. soil.

But the divisions are not on strict party lines, as some Democrats and libertarian Republicans have sought to negotiate an extension with stricter oversight and limits on when Americans can be monitored.

House Republican leaders backed off plans to vote on a long-term fix and instead extended the law until Jan. 19. Still, it’s unclear what the compromise legislation will look like, suggesting there’s still a danger the authority may be allowed to lapse.

Disaster aid. After passing the continuing resolution, the House passed legislation to provide $81 billion in new disaster aid for U.S. states, Puerto Rico and the U.S. Virgin Islands.

But in the Senate, Majority Leader Mitch McConnell, R-Ky., shelved the massive aid measure amid opposition from both parties. While Senate Minority Leader Chuck Schumer, D-N.Y., and other Democrats assailed that bill for not doing enough, fiscal conservatives have demanded its cost be offset by spending cuts elsewhere.

In a Dec. 21 floor speech, Texas Republican Sen. Ted Cruz harangued fellow lawmakers as they headed for the exits, saying Texas needs more aid.

“As jet fumes swirl around the halls of Congress and members head to the airports to head home for the holidays, I rise to remind my colleagues that there are still hundreds of thousands of people in Texas and Florida and in Puerto Rico who are still hurting from hurricanes Harvey, Irma, and Maria, and who will be spending Christmas not in their homes but in a hotel or with family and friends or in temporary housing,” Cruz said.

The bill, which nearly doubled the $44 billion request the White House sent to Congress, includes $434 million for the military’s hurricane response, as well as $28.6 billion for the Department of Homeland Security.

Immigration. Ever since President Donald Trump rescinded an Obama-era program to protect undocumented youth who illegally came to the country as children, Democrats and some moderate Republicans have pushed for a legislative fix. Without action, the program goes away in March.

Democrats in the House — but not the Senate — refused to vote for the last continuing resolution because it lacked a fix for the Deferred Action for Childhood Arrivals act. If Democrats did it before, they may again raise the issue alongside any new continuing resolution, using the threat of a government shutdown as leverage.

Joe Gould was the senior Pentagon reporter for Defense News, covering the intersection of national security policy, politics and the defense industry. He had previously served as Congress reporter.

More In Budget