WASHINGTON, July 4 -- The explosive claim buried in the Epstein files reads like a spy thriller: a confidential FBI source told federal agents that Jeffrey Epstein was a co-opted Mossad asset, that Alan Dershowitz had communicated directly with Israeli intelligence, and that Donald Trump had been "compromised by Israel." The document circulated across Washington and international newsrooms for weeks. Then someone identified the source.

His name is Charles C. Johnson. He once interned for Alan Dershowitz in high school.

The man who accused Epstein's most famous attorney of working for Israel's spy agency had, as a teenager, worked for that attorney himself. Johnson, founder of the now-defunct GotNews website and permanently banned from T...