I highly doubt much of the US military would defect, they generally love the country more than any particular political ideology. So you’d have a likely highly motivated military with more than half of the public on their side.
Then again, if this was a coup situation, I’m guessing it would be a bit more difficult, since some of the military would be on the side of the challenger. But that wasn’t what happened on Jan 6, Trump wasn’t calling on the military to keep him in office, he merely refused to call in reinforcements to deal with the insurrectionists.
I’m not saying it couldn’t happen here, I just think it would be incredibly difficult barring some kind of popular movement. And secession/insurrection isn’t popular.
If it was the difference between keeping the union together and falling into anarchy/fascism, pretty motivated.
