Subject: Re: The Coup Underway and Call to Americans
Then how can he fire them if they don't work for him? In a corporation (which the government isn't), a manager from a different department couldn't fire me.

Because the U.S. government isn't like a corporation. In the sort of corporation you're imagining, the managers from a different department couldn't set up the rules and make the policy decisions on what projects you work on either....but in the federal government, that role is given not to the Executive but to Congress. So too with budget and oversight.

That said, you can easily have a corporations where the power to fire is given to departments other than the one the employee works for.