One day in late May 2016, Roger Stone — the political dark sorcerer and longtime confidant of Donald Trump — slipped into his Jaguar and headed out to meet a man with a Make America Great Again hat and a viscous Russian accent. The man, who called himself Henry Greenberg, offered damaging information about Hillary Clinton, Trump’s presumptive Democratic opponent in the upcoming presidential election, according to Stone who spoke about the previously unreported incident in interviews with The Washington Post. Greenberg, who did not reveal the information he claimed to possess, wanted Trump to pay $2 million for the...