The armed forces pushed back on the transgender bane because they don't want to disrupt group cohesion, which is essential in a successful operation. But remember, the majority of soldiers are conservative, and if POTUS declared Left leaning groups as enemy combatants, they would be more than happy to oblige.
The next step would be removing anyone on the gov't who opposes him. Democrats, obviously, and any leaders of non partisan gov't offices that oppose his agenda on constitutional grounds would also be declared enemy combatants.
Then, if a group like antifa causes trouble, declaring marshal law could be justified. And it would just get worse from there. Anything action POTUS wants to take will be declared constitutional by a 7 to 9 Supreme Court. The Republicans who have played defense for him for so long will be too scared to oppose him at this point. (not that they ever had a spine...)
Russia will be made an ally, Europe, the enemy, and then the fun really begins.