“And tanks, and A-10s, and USMC rifle companies.”
What makes you think the Marines will join antifa, Maxine Waters and Hillary? And how do you fly an A-10 with no flightline crew?
There are two possibilities (as regards civil conflict).
If Trump is impeached and removed from office, presuming that there are 218 legitimate votes in the House to send articles to the Senate, and 67 validly electing sitting US Senators vote to convict, then, Mike Pence is sworn in, Mattis remains as SECDEF, the Joint Chiefs all support Pence and Mattis, and therefore the chain of command remains intact.
Under those circumstances, I believe that commissioned officers will follow orders transmitted through the chain of command and their troops will follow their officers.
And if armed civilians rise in rebellion, I believe they will be slaughtered. Easily.
The second possibility is a non-legal or extra-legal removal of the President, with him surviving (a coup). This is a distinct possibility. The Acting President (I presume Pence) would appoint a new SECDEF, and then you would have the situation which existed in April 1861, with commanders choosing sides and armies in the field.
In that case, all bets are off.