Vox - Trumps media allies are making the case for firing Robert Mueller

The last paragraph of Vox's analysis hits the nail on the head. There will be tremendous blowback if Trump fire Mueller even if Congressional Republicans are likely to give Trump a pass on such a move. However, what this means is that Trump believes that the blowback is less damaging then allowing Mueller's investigation to proceed.

https://www.vox.com/policy-and-politics/2017/6/12/15782092/fire-robert-mueller

When Richard Nixon did this in the Saturday Night Massacre it was a major scandal that, in many respects, kicked the Watergate investigation into overdrive. And, indeed, it was the political backlash to firing Comey that saddled Trump with the Mueller investigation in the first place. Prudent counselors might advise him that firing Mueller will only serve to further exacerbate his problems.

On the other hand, while firing Comey was not exactly well-received on Capitol Hill, the vast majority of congressional Republicans were eager to rally around the idea that Trump was within his legal rights to fire the FBI director. One clear takeaway from Comey’s public testimony last week is that congressional Republicans do not believe that asking an FBI director to stymie an investigation, then firing him when he doesn’t do it, then lying to the public about why you fired him constitutes obstruction of justice or abuse of power in the relevant sense.

Given that standard, they might well conclude that firing Mueller is okay too. Trump’s legal authority to do this, after all, is perfectly clear. The only check is political backlash on Capitol Hill, where Republicans hold majorities in both houses and have thus far shown little inclination to check Trump.

Last but by no means least, one advantage Trump has in Russia-related decision-making is that he knows more than either his allies or his antagonists in Congress about what the underlying facts of the case are. Trump is in a unique position to evaluate whether the political costs of a cover-up exceed the political costs of a thorough investigation. In the case of, for example, his still-secret tax returns and personal finances, Trump has decided that the cover-up is the wiser path — and it’s certainly possible he’ll reach the same conclusion with regard to Mueller.