As long as the Republicans controlled both houses of Congress—and as long as they refused to challenge or break from Donald Trump in any meaningful way—Capitol Hill was a land of make-believe.

All that changes next week, and I suspect that most Republicans, and most people in general, haven’t the slightest idea of how bad things may well get for the GOP. We could witness a schism over Trump that ultimately leads to the downfall of the party, akin to the Whigs of the 1850s, and yes, I’m being completely serious.

Let’s start with the immediate matter at hand, the government shutdown. When the 116th Congress convenes on Thursday, the House’s new Democratic majority will pass a bill to reopen the government, a bill that will include $1.3 billion for border security but whose dollar figure for border wall funding will presumably be zero. What will Mitch McConnell do?

You might think, well, he’ll just say this bill is a nonstarter because it has no wall funding—in other words, that he’ll stand pat with the president. The only problem with that is that the McConnell-run Senate approved the very same $1.3 billion for security/zero for the wall legislation already. In fact, it’s done so twice, once in the normal appropriations process and then again on Dec. 19 in the form of a continuing resolution to try to avert a shutdown.

It would be pretty hypocritical of McConnell to say now that he won’t support a bill that doesn’t have wall money (will he, like Kirstjen Nielsen, “need wall”?). Of course, hypocrisy has never bothered Mitch, so he might well say it. But that’s not really the Senate Republicans’ position (though House Republicans are mostly pro-wall).

I don’t want to get too down in the legislative weeds here. The larger point is this. There are deep divisions within the congressional Republican Party on the wall, which in turn reflect divisions about how nativist and xenophobic a party it should be. Trump is pushing the party to an extreme position that a number of them have rejected in the past. Remember, it wasn’t that long ago, just five years, that 14 GOP senators voted for comprehensive immigration reform that included no wall and a path to citizenship. That bill would also have passed the House, with maybe 30 to 40 Republican votes, if then-Speaker John Boehner had permitted a vote, but he never did.

We’ll see how Trump plays this in the coming days. If he digs in and takes radical steps like closing the border entirely, he’s going to force a deep split within the GOP on immigration. When they controlled both houses of Congress, they could find ways to paper over this. But with Democrats running the House and forcing votes that Republicans don’t want to take, papering over will no longer be possible.

And that’s just the appetizer. The entrée is the Mueller investigation.

Let’s say Mueller comes out with his report in the spring, and let’s assume for the moment that it’s devastating. Maybe it won’t be, but let’s say it is (which is what I think most people this side of Rudy Giuliani assume).

The Democrats in the House, with their new power, hold hearing after hearing, something Republicans of course would not have done. The newly indicted Trump associates start heading to court, or singing. Trump is clearly named as an unindicted co-conspirator on any number of fronts, from collusion to obstruction, and we learn officially that Russian banks own him and have for years.

His approval ratings fall. He acts even more erratically. There is serious talk of impeachment, supported not just by Democrats, but also a slight majority of independents. There is serious talk of the 25th Amendment option. There is serious talk of a major and well-funded primary challenge to him in 2020.

If all that happens (and maybe throw in a recession, too), how many Republicans will still be with him, say, a year from now? A majority, I think; but I also suspect there will be enough defections to matter.

In the 1850s, the Whigs collapsed because of internal tensions over slavery. The Northern Whigs were vehemently anti-slavery, and the Southern Whigs were strongly pro-slavery. The party was a strange amalgam of forces to begin with, less united around what they liked than what they hated, namely Andrew Jackson; so that’s one point on which any Whig-Republican analogy admittedly doesn’t hold up. Today’s Republicans are an ideologically disciplined and unified party, whereas the Whigs were not.

Still, Trump, in his childish vanity, makes everything about himself. And beyond that, these fights over Trump are about larger matters, too. The immigration fight is over the party’s stance toward one of the hallowed traditions of this country (that we are a nation of immigrants), and the Mueller fight is over the Constitution itself, and the rule of law.

Are those stakes as big as slavery was in the 1850s? You bet they are. In other words, how we treat immigrants and whether we remain a nation of laws are plenty big enough matters for a party to split into two over. And Trump, being Trump, will do everything he can to force the split. He will make the future of the Republican Party a loyalty test to him.

For decades, Republicans have fancied themselves the party of the rule of law. After all, that’s what a republic is by definition, a nation of laws, as opposed to a democracy, a nation of majority rule. But it’s also the case that in the last few years, the Republicans have become the party of sheer lawless power, from Bush v. Gore to the denial of Barack Obama’s 2016 Supreme Court pick to their blind loyalty to this mobster president.

Trump, inevitably, will force them to choose. And that is the exact fault line on which they may split. One part of me says this is bad for the country; the other part says pass the popcorn.