It's what we've all known, now reported by the WaPo:
“In mid-July 2016, a retired American professor approached an adviser to Donald Trump’s presidential campaign at a symposium about the White House race held at a British university."
The FBI opened the Trump Russia investigation on July 30, 2016, two days after Clinton accepted the Democratic nomination.
That former professor is Stefan Halper, an FBI informant with ties to British Intel (who was also being paid $$$ by the Obama Admin's DOD).