That’s not to say we’re completely out of other avenues. There’s the theory that Rosenstein could simply ignore any attempts to fire him, claiming that if he’s being fired for not shutting down an investigation by the very people under investigation, then that firing is improper and void. But that’s uncharted legal territory. And the courts could step in, and it could be a lovely mess. But frankly it’s not very good odds. State attorneys general can bring suits, New York seems likely already. You’ve got money laundering, racketeering, RICO, all the good stuff at their disposal. But since we’re on the topic of legally uncharted territory, the president may actually have the power to pardon himself (it’s never been tried), only matters of impeachment are explicitly barred–and state AG’s can’t impeach the president.