An elaborate hoax based on forged documents escalates the phenomenon of “fake news” and reveals an audience on the left that seems willing to believe virtually any claim that could damage Trump. In the third week of January, an Israeli named Yoni Ariel flew from Tel Aviv to Rome carrying $9,000 in cash on a secret mission to bring down Donald Trump. There, he met with an Italian businessman. Seated at a table toward the rear of a café, away from the street where they might attract unwanted attention, Ariel recalled, he handed over the cash. In exchange he was...