If there were a coup, maybe they could put the candidate who actually won the election (by 3 million votes) in the White House?
I really don't think the chances of a coup are high at all. I think there would be a lot of grumbling from Democrats (probably to a degree never seen before), and some from Republicans too, although not much; the rest of the GOP will back him to the end, or until their poll numbers and reelection odds take a serious dive (which would probably happen).
Trump's approval rating would go even lower (hard to imagine at this point, since he's already almost bottomed out). Pence would distance himself even more than he's doing now so as not to appear guilty of wrongdoing; Pence would also begin prepping himself to be sworn in as the 46th commander-in-chief.
I'm not sure what route it would take from there, but I do think that should Trump fire Mueller, his days as president are numbered. Should it happen prior to 2020, then he won't be a candidate for president in 2020. Either through impeachment, or just declining not to seek reelection, he would not appear on the ballot.
Also, Hillary Clinton would make another round on the airwaves telling the country, "I told you so." And she'd be right (again).
Many people were caught completely off guard in Chile in 1973, including the conservative democrats who had no idea of what to do in the wake of the coup. Chile has institutions similar to ours, and Trump is even more erratic than Allende.
I'd be wary of some of the more reckless talk of President Trump. "Calm before the storm"? The gusts are already zephyrs. People are starting to have shaky gaits.
More dangerous is any unilateral move by President Trump to start a war. North Korea? Iran? Venezuela?
The ambush of American soldiers in Niger (I am guessing that Boko Haram, a nasty organization with ideological ties to ISIS and similar ruthlessness and brutality) could get hit hard. That would be less troublesome, barring overkill.
...The likelihood of a military coup has been nil throughout all of American history until Donald Trump became President. It is now slight. That is a huge change. That's not to say that I want a coup. This country does not need or want a Pinochet. But I can imagine the Joint Chiefs of Staff making clear that senior military officers will not risk becoming war criminals in support of President Trump.
