REVEALED: GOP senator confronted Trump about apparent Ukraine quid pro quo in Aug. 31 call

Gordon Sondland, the U.S. ambassador to the European Union, told Sen. Ron Johnson earlier this year that he believed military assistance to Ukraine was directly tied to the country's willingness to launch investigations that were desired by President Donald Trump.

In an interview with the Wall Street Journal, Johnson claims that he then asked President Donald Trump if he had tied aid to the country with his desire to see it investigate former Vice President Joe Biden, and the president denied the claim.

“He said -- expletive deleted -- ‘No way. I would never do that. Who told you that?'" the Wisconsin senator tells the Journal.

Sondland, a Trump megadonor who was confirmed as America's E.U. ambassador last year, has emerged as a key figure in the Ukraine scandal that has engulfed the White House. Newly revealed text messages show that Sondland believed that Ukraine would have to agree to investigate Biden as a precondition for a White House meeting between Trump and Zelensky.

In one particularly exchange, veteran diplomat Bill Taylor told Sondland that it was "crazy" to tie Ukrainian military assistance to the country helping the president's electoral prospects. Sondland then sent back a text message denying any quid pro quo -- and then urging Taylor to take the discussion offline.