They attempted to impeach Clinton, and there was no civil war. So if the same happens to Trump, I highly doubt we will see hand to hand combat in the streets.
It's more that it simply wouldn't happen. How long since one of the parties has had a 2/3 majority in both House and Senate? So realistically some Republicans would have to vote to convict him. Which would make the Republican Party go the way of the Whigs. Only the Tea Party faction is crazy enough to destroy their own party for some (perceived) larger principle, and they'll be on Trump's side.
As Louis Thoreau said, Trump's genius is that in a country with a culture of shame, he is utterly shameless - and people love him for it. He could fuck a goat on the White House lawn while reciting a copy of
Das Kapital and his supporters would still love him. Any conviction by the Republicans would be taken as a betrayal of all the voters, and the party would implode and fizzle into non-existence, with some new party appearing in their wake.
So it simply won't happen. He can get impeached, but he won't be convicted. Which means if they have any brains they won't bother impeaching him - trying and failing would hurt his opponents more than him.
As the other guy said, division is good for the market, because division means inaction, which means greater certainty for business. Business can adapt to virtually any combination of taxes, subsidies, tariffs, and regulations, what fucks it all up is things changing all the time. A while back Belgium went like two years without a functioning government (they couldn't cobble together a majority in Parliament, so just had a caretaker government that did nothing) and their economy boomed.