The president was pleased by the ambiguity of his position on Mr. Mueller, and thinks the possibility of being fired will focus the veteran prosecutor on delivering what the president desires most: a blanket public exoneration.
Trump thinks Mueller's investigation, like Comey's, is a "witch hunt," and if he cuts off Mueller as he did Comey, it goes away. But also, he doesn't care about the investigation except as it implicates him. A "blanket public exoneration" is precisely what he demanded of Comey. Obstruction of justice, in other words. But he can't be obstructing justice if he's just getting a declaration that he's never responsible for anything, can he?
Of course, to Trump, the word means "just us." He doesn't even care about the government. He just cares about Donald Trump.
And away with the "Will he/won't he?" speculation. He will, at the drop of a hat (the White House insists it can if it wants to. Reasonable analysis says Trump will have to go through Rosenstein to get there, and there may even be a problem if enough appointed people refuse to play Robert Bork this time around. Trump's incompetence in staffing may, in the end, prevent him from firing Mueller without a court fight.) Recall, too, it wasn't the Saturday Night Massacre that did Nixon in. Bad as that was, Nixon wasn't done for until the tape came out.
I don't need Nietzsche to explain this to me. The good ol' Christian concept of sin, which has at its root human selfishness, tells me all I need to know. That concept explains both Trump, and the willingness of some to see him as more sinned against than sinner. I also don't care anymore who replaces him; this guy shouldn't be allowed in the White House for a public tour.