Let’s start with Justice. Because Sessions recused himself from the Russia investigation, an order to fire Mueller, for now, would go to Deputy Attorney General Rod J. Rosenstein — who has strongly indicated that he would refuse. In June, members of the Senate Appropriations Committee got this commitment: “I am not going to follow any orders unless I believe those are lawful and appropriate orders. Special counsel Mueller may be fired only for good cause, and I am required to put that cause in writing.”

Can Congress obtain similar pledges from other senior officials of the Justice Department who would be in the chain of command? During the Watergate scandal, Attorney General Elliot Richardson and his deputy, William Ruckelshaus, felt bound by the commitments they had given Congress not to fire special prosecutor Archibald Cox. A similar chain of obligation should be forged now, to circumscribe Trump’s ability to sack Mueller.