Senator Chris Murphy of Connecticut, a Democratic member of the Senate Foreign Affairs Committee, said he warned the Ukrainian government not to meddle in America's electoral process days before it was revealed that President Trump sought to enlist the help of that country's leader to dig up and disseminate dirt on a political rival.

"When I went to Ukraine three weeks ago, I told the president that he should stay away from interfering in the 2020 presidential election," Murphy said on "Face the Nation" Sunday, referring to Ukrainian President Volodymyr Zelensky. "And if he wants to talk to the United States government, he should talk to the State Department."

The Connecticut Democrat said he discussed the matter with Zelensky because he was aware of concerns that the Ukrainian government had about requests from Mr. Trump and his personal attorney, Rudy Giuliani, to investigate former Vice President Joe Biden and his son, Hunter, who used to sit on the board of natural gas company there.

A whistleblower complaint filed earlier in the summer and declassified last week detailed how Mr. Trump pressured Zelensky to order a criminal probe into the Biden family during a phone call in July. The allegation, corroborated by a memorandum of the conversation released by the White House, prompted House Speaker Nancy Pelosi to announce a formal impeachment inquiry into Mr. Trump's actions.

The complaint also denounced a rogue diplomatic effort by Giuliani to exert pressure on the newly elected government in Ukraine. The whistleblower said top U.S. diplomats became involved in Giuliani's outreach and helped broker a meeting he had with one of Zelensky's advisers.

Although it has confirmed that the top U.S. envoy to Ukraine at the time helped arrange the meeting, the State Department said Giuliani did not speak "on behalf" of the U.S. government.

But Murphy said it is clear that Giuliani was exploiting his important connection to the president to portray himself as an arm of America's diplomatic corps.

"You can understand how the Ukrainians are confused when the personal representative of the president is coming to them and asking them to help destroy one of his political rivals," Murphy said. "And you can also understand how they might be concerned that if they don't do the bidding of the president of the United States there might be consequences that come to them."