On Thursday, President Donald Trump finally broke his second-term “no scalps” rule, announcing that D.H.S. Secretary Kristi Noem would be leaving the job and replaced by Oklahoma Sen. Markwayne Mullin. Noem, of course, was the controversial face of Trump’s immigration crackdown, who not only rushed to label two Americans “domestic terrorists” after they were killed by federal agents in Minnesota, but also took heat for more prosaic petty corruption and mismanagement: spending taxpayer money on luxury planes, directing departmental contracts to her associates’ spouses, and allegedly sleeping with a subordinate. (Noem and Corey Lewandowski have both repeatedly denied having an affair.)