This is the story of a congressional staffer who committed a crime, and a larger crime that was committed against him. It’s a story of a fever on Capitol Hill, spiked by right-wing extremists with help from President Trump. Last year, a congressional information-technology staffer who worked for more than a dozen Democratic members of Congress (a permissible and customary practice on Capitol Hill) was suspected of using multiple usernames and passwords to skirt House rules and purchase office items. This isn’t exactly the stuff of gripping television crime drama. But rules were broken and the staffer, along with four...