WATCH: Trump's own Russia ambassador nominee admits it's wrong to ask Ukraine to investigate Joe Biden
Deputy Secretary of State John Sullivan (Screen cap).

United States Deputy Secretary of State John Sullivan, who has been nominated by President Donald Trump to serve as America's ambassador to Russia, told members of the Senate on Wednesday that it's wrong for presidents to ask foreign governments to investigate their political opponents.

During testimony before the Senate Foreign Relations Committee, Sullivan was asked if it was ever right to ask the leader of a foreign government to launch investigations into political rivals.

"Soliciting investigations into a domestic political opponent -- I don’t think that would be in accord with our values," Sullivan replied, according to the Washington Post's Aaron Blake.

Also during his hearing, Sullivan admitted that he saw no concrete reason to fire ousted former Ukrainian ambassador Marie Yovanovitch, but he said that he couldn't simply have kept her in her position once the president had lost confidence in her ability to serve.

"When the President loses confidence in the ambassador, right or wrong, the ambassador needs to come home," he said.

Watch the video below.