In my opinion it would largely be a form of guerrilla warfare. ...
There would be plenty of attacks on the infrastructure of our nation including the power grid, the rail system and the interstate highway network. A good number of people in our nation have served in the military and a significant number of those have combat experience in war zones and therefore have a good understanding of guerrilla tactics as they experienced it.
Also keep in mind that Americans own 50% of all the guns in the world.
(Source: https://www.theatlantic.com/politics/archive/2012/12/guns-in-america-statistics/320409/)
Of course some states would secede from the Union and likely split the nation down the middle rather than north and south.
It would be one hell of a mess. Fortunately I don't feel that at this time we are anywhere close to an uprising. We are living in a very contentious time frame but our nation has lived through such times and held together since the Civil War. I suspect we will once again resolve our political disagreements at the ballot box.