The active military get paychecks. If shooting Americans starts, there'll be a divide. Red state white boys are a lot of combat arms. The Reserves and NG, is regional, individual and not so reliant on the paycheck. Not all cops are maga assholes. Choices will be made. Families safety a priority.
There also aren't enough of them, even if all go along. It takes at least 25 of our troops per 1000 people to maintain an occupation, if the population is compliant. If armed, 50-60 per 1000, and rural areas are worse.
Aye in the UK at least... not every cop joined up because they like battering folks. I doubt it's true in the US as well. Even those who did will resent being told what to do by these fascists We need an acronym.. NACAB?