Sen. Mitt Romney, R-Utah, who has at times been a critic of President Trump, on Friday accusing the president of "appalling" behavior in his call for China and Ukraine to investigate former Vice President Joe Biden and his son Hunter.

"When the only American citizen President Trump singles out for China’s investigation is his political opponent in the midst of the Democratic nomination process, it strains credulity to suggest that it is anything other than politically motivated," Romney tweeted.

He added: "By all appearances, the President’s brazen and unprecedented appeal to China and to Ukraine to investigate Joe Biden is wrong and appalling."

ROMNEY CALLS FOR 'FACTS TO COME OUT' AFTER UKRAINE SCANDAL

Romney's comments came amid an official impeachment inquiry in which House Democrats have accused the president of trying to interfere in the 2020 election.

Trump's team has maintained that the president's attempts to influence Ukraine to investigate the Bidens' business activity in that country were a legitimate exercise of the president's authority.

Romney's comments were just the latest in a series of criticisms the former Republican presidential nominee has lobbed at the president.

Shortly after details surfaced about Trump's July call with Ukraine, in which he is said to have urged its president to probe the Bidens, Romney called for additional facts and claimed Trump's reported comments sounded "troubling in the extreme."

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Giuliani responded to Romney by accusing him of being "bitter" about Trump. "Look, Mitt, Trump did what you couldn't do. Trump has an ability to relate to people -- you don't," GIuliani said at the end of September.

At one point in 2019, Romney drew a rebuke from his niece Ronna Romney McDaniel, who serves as the chairwoman of the Republican National Committee. The senator had penned an op-ed in which he attacked Trump's conduct, saying he "has not risen to the mantle of the office."