In the shifting narratives of the Trump-Russia probe, a Maltese academic named Joseph Mifsud has remained a linchpin regarding claims of collusion. He is the professor who allegedly told Trump campaign adviser George Papadopoulos that the Russians had emails related to the Clinton campaign. The FBI says it opened its investigation in late July 2016 after Papadopoulos relayed that information to Australian diplomat Alexander Downer, and the Australians tipped off U.S. authorities. While some news accounts describe Mifsud as an accomplice to Russian clandestine operations or a “cut-out” (intermediary), others contend he is a full-fledged Russian spy. In an official...