Robert Mueller’s investigation of Donald Trump has kicked into higher gear, with witnesses being called before a grand jury, new demands for information from the White House, probes of the connection between the Trump family business operations and his official decisions as president, as well as a deepening investigation of ties with Russia. One can only imagine how all this grates on Trump.

Deputy Attorney General Rod Rosenstein, directly contradicting Trump’s fishing expedition claim, says Mueller can investigate any crime that he uncovers in the course of investigating Russian influence in the 2016 campaign.

As the water keeps rising around Donald Trump, it is impossible to believe that Trump will not escalate his campaign of vilification of Mueller and his associates. Trump is happiest firing people who get in his way. The intriguing question is what the new White House chief of staff, John Kelly, will do if Trump cannot stand it any more and impulsively tries to fire Mueller.

That question must have come up in the prolonged discussions between Trump and Kelly before Kelly finally agreed to take the job. I was not in the room, but there is strong circumstantial evidence that Kelly told Trump that he would not stand for Mueller’s dismissal.

For starters, Kelly has strongly and publicly intervened to protect another Trump nemesis, the embattled Attorney General Jeff Sessions.

Last week, Kelly contacted Sessions and assured him that his job was safe, directly contradicting earlier threats by Trump. And just to be sure that Trump doesn’t attempt a firing and recess appointment of a successor attorney general, Republicans in the Senate have warned Trump that no successor would be confirmed.

Sessions, however, has recused himself from the investigation of Trump. If Kelly has gone out his way to protect Sessions, he would surely do the same for Mueller.

Another clear signal: Someone let it be known around the time of Kelly’s appointment that Kelly had called former FBI chief James Comey to express anger and dismay at both the manner and the fact of Comey’s abrupt dismissal by Trump.

Again, it would be wildly inconsistent if Kelly were to sit still for the even more consequential firing of Muller.

So Kelly very likely made clear that ousting Mueller would be a deal breaker for his own relationship with Trump. Kelly also got assurances that everyone in the administration would report to him, even Jared Kushner and Ivanka Trump.

So far, Kelly has won high praise for cleaning up the chaos at the White House and being part of every major conversation and decision. But here’s the rub. Donald Trump is not as good as his word, and he can’t control his impulses. He also is addicted to offline conversations. Jared and Ivanka may report to Kelly during office hours, but the new chief of staff can’t stop Trump from talking with his daughter and son-in-law at other hours of day or night.

Trump is paranoid during normal times, but as the saying goes, even paranoids have real enemies. By definition, Mueller is an existential threat to the Trump presidency.

As the noose keeps tightening, Trump will become even more unhinged than usual. Some sort of showdown seems inevitable, which could end with Kelly resigning, Congress trying to block Mueller’s firing, or the immediate creation by Congress of a new special counsel beyond the reach of the White House. Alternatively, Mueller could survive long enough to deliver a bombshell report.

In the meantime, there has been a stunning series of Republican defections. These will only intensify if Trump tries to go after Mueller.

Once the repeal of Obamacare failed, Republicans under the leadership of Tennessee Senator Lamar Alexander began reaching out to Democrats to fix the very real problems in many insurance markets — to strengthen the program not kill it. Republicans also compelled Trump to sign legislation removing his ability to suspend sanctions against Russia, and effectively blocked his ability to replace Sessions.

The GOP has had a bellyful. Key Republican leaders have warned Trump not to mess with Mueller. But my guess is that he won’t be able to stop himself. And there could well be other conflicts where Trump begins to doubt Kelly’s basic loyalty.

In the past two weeks, Trump’s firewall of Republican partisan protection has begun to crumble. The conventional wisdom has been that a Republican Congress would never impeach Trump. This could change abruptly.

Since Trump’s election, I’ve been of the view that he won’t last two years. That seems more evident than ever.

Robert Kuttner is co-editor of The American Prospect and professor at Brandeis University’s Heller School. His latest book is Debtors’ Prison: The Politics of Austerity Versus Possibility.

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