In an interview this week, Andrii Telizhenko said he met with Johnson (Wis.) for at least 30 minutes on Capitol Hill and with Senate staff for five additional hours. He said discussions focused in part on “the DNC issue” — a reference to his unsubstantiated claim that the Democratic National Committee worked with the Ukrainian government in 2016 to gather incriminating information about then-Trump campaign chairman Paul Manafort. Telizhenko said he could not recall the date of the meeting, but a review of his Facebook page revealed a photo of him and Johnson posted on July 11…

More significantly, testimony from two blockbuster witnesses in the impeachment probe place Johnson at episodes that will be critical in assessing whether Trump was withholding nearly $400 million in congressionally appropriated military aid to Ukraine in exchange for political favors. Ukrainian President Volodymyr Zelensky faced pressure to announce investigations into the Bidens and the debunked conspiracy theory that a hacked DNC server was taken to Ukraine in 2016 to hide evidence that it was that country, not Russia, that interfered in the presidential election.

Johnson’s knowledge of key events could make him a person of interest to House impeachment investigators, as well as complicate his role as a juror in a trial by the Senate, if one occurs. There are no rules forcing senators with possible conflicts of interest to recuse themselves during impeachment proceedings, and Johnson, through a spokesman, declined to comment on what he would do.