The Justice Department is investigating how a former British intelligence agent, Christopher Steele, came to exert so much influence over the Federal Bureau of Investigation’s erroneous Trump-Russia collusion narrative. Let’s hope the department is also investigating an even more influential man who had even less business manipulating the government: Glenn Simpson, the head of opposition-research firm Fusion GPS.

That’s a pressing question in light of new documents from high-ranking Justice official Bruce Ohr, obtained recently...