Trump "Ordered" Mueller Fired (?)...What's The Chain Of Command?

Depending on the nature of the chain of command...which I know nothing of...if Trump was going to fire Muller, wouldn't he just fire him? I mean, if you serve at my pleasure, directly, what would it mean to say that I "ordered" you fired? Don't I either fire you or not fire you? Myself? Directly?
   Again, not saying the tale isn't true...just saying I don't trust the media about Trump anymore, and that this sounds a little fishy to me.
   I've long said that if he tries to fire Mueller, the shit should hit the fan...but I wasn't sure what I meant, and now I'm even less sure. Partly because I'm not sure what I meant by tries to fire. Obviously the former should hit the latter if he does fire him...or if he diligently does his best to do so but, say, Mueller is saved by some kind of technicality. But if it's just more Trump bullshittery--throwing a tantrum and yelling about firing him or whatever...well, that's a whole different kind of problem, IMO.