Sometime in the next month, Congress could come to the brink of shutting down the government.

Congress has to pass some sort of spending bill by Dec. 8 to keep the lights on, but they may just kick the can down the road until Christmas.

“I believe the odds are better than 50 percent,” said Steve Bell, a former GOP budget aide now with the Bipartisan Policy Institute.

There are just too ways things could go wrong: a contentious tax debate; intractable policy fights over immigration, health care and spending; and an unpredictable president who, on Tuesday morning, signaled he’s not willing to compromise with Democrats.

“Meeting with “Chuck and Nancy” today about keeping government open and working. Problem is they want illegal immigrants flooding into our Country unchecked, are weak on Crime and want to substantially RAISE Taxes. I don’t see a deal!” President Donald Trump tweeted Tuesday before that meeting was cancelled.

There’s so much going on that could trip up Congress, so we ranked the five likeliest scenarios that could shut down the government.

5. Republicans don’t pass a tax bill by Christmas

Republicans would like to pass a major tax rewrite before they focus on a spending bill. The Senate plans to vote this week on a tax bill, but even if that passes, the Republican is only halfway done: The House and Senate would still need to align their respective versions of very different bills, then vote again on a compromise.

Republicans are trying to do all this without Democratic votes, and they have little room for error. In the Senate, they can afford to lose two votes. More than half a dozen Republican senators have expressed concerns with it.

When (or if) the tax bill passes, it will determine the rest of Congress’s schedule, said Stan Collender, a nonpartisan budget expert and columnist for Forbes.

“If it passes by end of December the chance of a shutdown is zero,” he told The Post in an email. Republicans won’t want to take away from their big accomplishment by shutting down the government on their watch. “If it doesn’t, the chance is over 75 percent.”

Why? Because, President Trump is increasingly anxious for a legislative win, and Trump could hold up the spending bill as a chance to force Republicans to do something big by his first year. “This will be a signature political moment for Trump if he gets to shut down the government because he didn’t get a tax bill by his deadline,” Collender predicted.

4. Republicans try to undo major parts of the Affordable Care Act

Actually, this is already happening. The Senate tax bill would repeal the crux of Obamacare, the individual mandate that says most people must have health insurance or pay a fine.

There’s not much Democrats can do about it since Republicans are trying to pass the tax bill without their support. But angry Democrats could exact punishment on the spending bill, where Republicans likely need their votes.

Trump inflamed this very delicate situation when he urged Republicans to repeal all of Obamacare after they pass a tax bill. That’s not likely to win over any skeptical Democrats.

3. Democrats demand protection for dreamers

Part of the reason Congress’ to-do list this month is so long is because Trump has ended a number of Obama-era policies and kicked their future over to Congress. He shut down the Iran nuclear deal, cancelled federal payments that keep Obamacare viable for lower-income Americans, and ended deportation protections for young undocumented immigrants.

That last one seems to be the sword Democrats are willing to fall on this December.

The Post’s Mike DeBonis and Ed O’Keefe report that dozens of liberal lawmakers will refuse to vote for a spending bill if it doesn’t provide legal protection to dreamers.

2. Republicans and Democrats can’t compromise on spending levels

Funding the government is difficult. Funding the government on a budget is really difficult. And Congress has been on a strict budget since 2011, when they created self-imposed spending caps as part of another budget deal.

This year, Trump and Republicans want to bust through those caps to beef up military spending by more than $600 billion. But Democrats want something else in exchange for their votes: boosting spending for the military and domestic priorities equally.

This has been one of Democrats’ red lines for as long as spending caps have existed, so Republicans and Trump are likely going to have to compromise here or risk losing Democratic votes.

1. Trump himself

Not being able to predict Trump is Congress’ biggest hurdle.

No one knows what he wants or who he’ll side with, even after he makes his decision. This September, he sided with Democrats over a budget and debt ceiling showdown and agreed to discuss protecting dreamers. Then he flipped his position on immigration several times in one day.

There’s always a chance he’ll demand money for a border wall, which is a non-starter for Senate Democrats and a lot of Republicans.