Only congress is supposed to be able to authorize the creation of new departments.

Assuming congress cares about their role in checks and balances, they are the branch the creates and destroys federal agencies and departments. But if congress is asleep at the wheel (hypothetically of course, since surly they’d never do such a thing), a president could reassign an existing agency to completely change their mission and allow them to take full control of other agencies in a bid to exert maximum executive control outside the bounds of constitutional frameworks.

Not that this sort of thing would ever happen since surely the judiciary would step in to note it’s unconstitutional and congress would quickly remove from office any executive that attempted such a blatant power grab…