Thinkable
By 
Team Trump is floating the idea of firing Robert Mueller. I agree it’s very possible, and these are the most compelling reasons:
First, Trump has a very strong motive to fire Mueller: he is probably guilty. Several of Trump’s associates have obscured or lied about their meetings with or financial ties to Russia, Trump has taken a curiously pro-Russian approach to a series of diplomatic issues (including handing over sensitive information to Russian diplomats), and his son-in-law tried to establish a secret communications line to Moscow. Even if Trump and his inner circle turn out to be innocent of the underlying crime, he is obviously guilty of obstructing justice: demanding loyalty of the FBI Director, asking him to halt an investigation into a presidential crony, asking other intelligence officials to make this request as well, firing him, and then publicly admitting he did it to quash the Russia investigation is comically transparent fact pattern.
Trump continues to take actions that are difficult to explain if he is innocent and only sensible if he is guilty. A year ago, it seemed implausible to imagine that he could actually make it through the campaign without releasing his tax returns. What could he possibly have to hide that would be worse than the appearance of guilt he was inviting? Perhaps the answer is the same as why he might fire Mueller. What would be worse than the backlash from firing Mueller? The outcome of Mueller’s investigation, maybe.
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Third, Trump has endlessly violated a series of norms that appeared to be inviolable. From the outset of his candidacy, party officials warned him that his behavior – the absurd and promiscuous lying, refusal to disclose his tax returns, refusal to divest his business interests as president, undisciplined tweeting, and on and on – would have to stop.
These experiences have taught Trump that the caterwauling Republicans have no real power to hold him back. He can accuse Ted Cruz’s father of killing Jack Kennedy, and call his wife ugly, and however angry he gets, Cruz will come crawling back. Republican warnings have always proved empty.
Why should the firing of Mueller play out much differently than the firing of Comey? The pro-Trump right will back him enthusiastically on Fox News and talk radio. The anti-anti-Trump right, a smaller and weaker faction, might initially object, but will quickly turn its attention to quibbling with or mocking his critics. (Get a load of this Berkeley professor who says firing Mueller is like the Reichstag fire! Or what about the time Bill Clinton or Barack Obama did something bad?)
Admittedly, there are some elements of a scenario where Trump fires Mueller that are a little tricky to game out. Such as, how many congressional Republicans will express concern as they do nothing about Trump, how many congressional Republicans will say that they’re disturbed as they do nothing about Trump, and how many will not even pretend to give a shit as they do nothing about Trump? Tough question!