The Looming Constitutional Crisis

Trump now has an attorney general, like a human block of granite, who sees few limits on presidential power and is willing to obfuscate and execute blocking movements on his behalf.
While Republicans would ensure Trump survives a Senate trial, Democrats could still force vulnerable GOP senators to put their careers on the line and beckon history's judgment to defend the President. (CNN)

Barr is right to say that the president has broad authority to remove executive officers. The attorney general serves at his pleasure. But that doesn’t deprive Congress of the authority to say that if a president fires a subordinate with the specific intention of preventing investigation of his own criminal actions — well, that’s itself a crime. (Bloomberg Opinion)