Congress left town after passing the GOP tax bill, but left much else unresolved — meaning its already long to-do list over the next couple of months is even worse than expected.

The bottom line: The first items on the agenda will be immigration, a government spending bill and a budget caps deal, health care, and an expiring surveillance program.

January:

• Spending caps: Appropriators are still trying to reach a deal on discretionary and defense spending levels. Democrats don't want to raise defense spending caps without an equal increase in domestic spending.
• Immigration: Senate Majority Leader Mitch McConnell told reporters before recess that, if there's a bipartisan agreement that the administration also supports, legislation addressing DACA, or people brought to the U.S. illegally as children, will be taken up by the Senate. It would also likely include some kind of border security measure.
• Surveillance: The major Section 702 surveillance law — used by the intelligence community to justify warrantless surveillance of electronic communications of foreign nationals located abroad —expires in mid-January, thanks to a short-term extension Congress passed before leaving for the holidays. That debate pits hard line intelligence hawks against people like Sen. Rand Paul and Sen. Ron Wyden, who have threatened a filibuster when faced with the prospect of a long-term extension of the law. In the middle are lawmakers who are pushing for light reforms that won't satisfy the privacy advocates.
• Health care: Sen. Susan Collins, in exchange for supporting the tax bill, was promised a vote on both her reinsurance bill and the Alexander-Murray bill funding cost-sharing reductions. She didn't get either in December, and will be looking for both to be part of the must-pass government funding bill this month.
• Government funding: Once again, we're facing a shutdown if Congress doesn't pass a spending bill, this time by Jan. 19. If Congress gets a spending caps deal in time, then we're likely looking at a more thorough spending bill. If not, they'll probably have to pass another temporary continuation of current funding levels.
• Disaster relief: Lawmakers from Texas and Florida, both hit hard by hurricanes last year, are anxious to pass a multi-billion disaster relief package.

Beyond that, Congress still has to address:

• The Children's Health Insurance Program: Funding officially expired at the end of September, and it wasn't until December that Congress passed a short-term funding continuation (although states hadn't yet run out of money). But a longer-term solution still must be found, including ways to pay for it.
• The debt limit: The "extraordinary measures" being used to pay the country's bills are likely to run out sometime in the spring, and then Congress will have to act to raise the debt limit. This could be the last and greatest leverage point for House conservatives upset about all the money being spent.
• Extension of expired tax credits: There's been a lot of chatter about these happening in January, but they can also be made retroactive, giving Congress more time. There will surely be a strong push to delay some Affordable Care Act taxes, if they aren't addressed in a spending bill. The energy world is also watching these.Senate Finance Committee Chairman Orrin Hatch, just before the break, floated a bill covering energy efficient homes and buildings, biodiesel, geothermal energy, fuel cells and much more.Hatch's proposal also extends the availability of a production tax credit for new nuclear power projects, which is important for utility giant Southern Company's efforts to complete a delayed, over-budget reactor project in Georgia. Another provision boosts credits for carbon capture and storage initiatives.

Wild cards that could complicate an already-chaotic agenda:

• Iran: After the Trump administration's decision to decertify the Iran deal, Congress may choose to add new sanctions — which would almost certainly scuttle the agreement.
• FY2019 budget/reconciliation: Congressional Republicans may try to pass a 2019 budget, which is routine. However, there's a huge outstanding question of whether the budget will include reconciliation instructions and whether those instructions would start the process of partisan welfare reform, Speaker Paul Ryan's preferred agenda. However, McConnell has said he doesn't think welfare and entitlement reform should be done on a partisan basis.
• Infrastructure: The administration and McConnell want to pass an infrastructure package, but a plan hasn't been released, and any significant package will cost a lot of money — following the GOP's $1.5 trillion-dollar tax bill.