One of the deepest, darkest secrets of Russiagate soon may be unmasked. Even President Trump may be surprised. Multiple witnesses have told Congress that, a week before Trump’s inauguration in January 2017, Britain’s top national security official sent a private communique to the incoming administration, addressing his country’s participation in the counterintelligence probe into the now-debunked Trump-Russia election collusion. Most significantly, then-British national security adviser Sir Mark Lyall Grant claimed in the memo, hand-delivered to incoming U.S. national security adviser Mike Flynn’s team, that the British government lacked confidence in the credibility of former MI6 spy Christopher Steele’s Russia collusion...