Um, almost nothing in this country. It hasn't happened since the Whigs. That's W-h-i-g-s, but the irony is fitting. That was over the party's inability to grapple with slavery, which was centrally a policy schism. This... isn't policy. While the Republicans are divided over trade and immigration, that isn't why Trump is feuding with Paul Ryan, John Thune and the other party leaders. The Republican Party is in a state of civil war because they nominated the worst candidate ever.
But, that creates a different problem. Once Trump loses, and he will lose unless something big happens in the next 26 days, the problem will be the conflict between Republican leaders and Trump's voters. Back in August, I posted this about how the question going forward will be what happens with Trump's voters after he loses. I was pretty dismissive of claims that the Republican Party might collapse. I'm only slightly less dismissive now.
Here's the problem. Trump, for all his business bluster, isn't what I call a "Chamber of Commerce" Republican. Chamber of Commerce Republicans want low taxes, minimal regulation and stability. Trump has no coherent policy beliefs because he has never thought coherently about policy before. His newfound belief in tax cuts is what he adopted after Republicans flocked to him for his leadership of the birther movement, and beyond that, Trump's inherent instability makes Chamber of Commerce Republicans look at him like a ticking time bomb. Combine that with Trump's nativist and isolationist platform, adopted out of convenience to go along with birtherism, and Trump wound up putting not just himself, but his voters directly at odds with the Chamber of Commerce.
And that's the real problem. He exposes a fissure that has been suppressed for a long time. The real problem once he loses isn't really that he whines about the election being rigged. I've tackled that one before. The biggest problem for the Republican Party is that he keeps his supporters agitated against their own leadership, and now that the feud is going full steam ahead, that is almost certain.
Remember, for all Trump's sinking chances, he's still popular with a big chunk of the Republican electorate. And he can command press attention, even after he loses, to a degree that most losers cannot. Think of Mitt Romney. Remember that guy? Once he lost, his ability to draw media attention dwindled. Do you think that will be the case with Trump? Nope. So, what happens if Trump decides not to stir up violence and try to lead a revolution, but instead to extract vengeance on Republican Party leadership for betraying him on the premise that if they had stuck with him, he would have won? Trump, unlike normal losing candidates, will get press attention, and Trump, unlike other losers, will have a following. What happens to the Republican Party if he keeps whining about how Ryan and others stabbed him in the back?
I don't know. Parties are remarkably stable and solid. They have survived a long time, and endured a lot. Can Donald Trump bring down the Republican Party? Probably not.
Then again, this year is nuts.