I don't know whether this applies here or not, but when I heard that Mrs May had appointed BoJo as her foreign secretary I was reminded of something Lyndon B Johnson allegedly said about J Edgar Hoover shortly after becoming president. The context was whether it was finally time to retire - or rather forcefully dislodge from his throne against his will - JEH.
LBJ deceided against it, arguing he'd rather have JEH inside his tent pissing out than outside his tent pissing in.