If the president shreds the constitution, there would likely be many in the military opposed to it.

While they are actively replacing cabinet positions with loyal outsiders that have little-to-no experience within the organizations they now run (eg Patel, Hegseth), I think it’s reasonable to assume that there remains career leaders throughout that would put country before king.

You also need to look at loyalty within the rank and file of course.

When I talk to conservative friends about this scenario they generally laugh; of course the military would choose country over king. At least for now I think there remains enough institutional integrity that this is plausible.