Ok putting aside the obvious that 99% of US Military service members honor their oath to the Constitution and respect the chain of command serving the sitting President regardless of politics. Not least of which the DOD has been purging insurrectionist sympathisers the past few years.

So the brass tax of the US Military, our most valuable assets by a LOT are the US Navy. 2nd would be the USAF. Primary of which is arguably our Submarine force, followed by our sea warfare, then our air forces, and the rest of our nuclear arsenal.

Our largest sub base is in CT (blue).

The entirety of our carrier fleets are based in blue states - California, Hawaii, Virginia (blueish).

A significant portion of our nuclear stockpile is in Colorado (blue).

Anyway it all doesn't matter because any insignificant numbers who would defect would be nowhere near the command of these critical assets. The only real annoyance of Texas seceding would be having to relocate NASA HQ lmao.