The Federal Bureau of Investigation reportedly opened a counterintelligence investigation in 2017 to find out if President Trump was a Russian agent. What if the FBI had similarly looked into whether President Obama was an agent of Iran?

Counterintelligence agents would have examined the target’s personal and professional networks. The FBI investigated at least four Trump campaign figures for supposed ties to Russia. Only one, Mike Flynn, worked in the administration, and for less than a month. The Obama administration had...