Can’t the executive branch do whatever it wants?

Yes, technically/legally there’s checks and balances put in place to prevent any branch from getting too powerful, but the executive branch is the one with all the real power. That’s the police, FBI/CIA/etc, and especially the military. couldn’t the military just take over the country and establish their power over the other branches, rendering them useless? Written from the perspective of an American, but a question that I think can be applied to many countries.