In the fall of 2016, a little more than a month before Donald Trump was elected president, Christopher Steele had the undivided attention of the FBI.
For months, the British former spy had been working to alert the Americans to what he believed were disturbing ties Trump had to Russia. He had grown so worried about what he had learned from his Russia network about the Kremlin's plans that he told colleagues it was like "sitting on a nuclear weapon."
He was now being summoned to Rome, where he spent hours in a discreet location telling four American officials - some of whom had flown in from the United States - about his findings.
The Russians had damaging...