President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE lashed out at Sen. Mitt Romney Willard (Mitt) Mitt RomneyCrenshaw looms large as Democrats look to flip Texas House seat The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election Trump dumbfounds GOP with latest unforced error MORE (Utah) on Saturday and called him a "pompous 'ass'" after the Republican senator criticized Trump over his dealings with Ukraine.

"Somebody please wake up Mitt Romney and tell him that my conversation with the Ukrainian President was a congenial and very appropriate one," Trump asserted in a tweet.

Trump maintained that his public call this week for China to also investigate former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE "pertained to corruption, not politics."

ADVERTISEMENT

"If Mitt worked this hard on Obama, he could have won. Sadly, he choked!" Trump added, mocking the 2012 GOP presidential nominee for losing the election to former President Obama.

"Mitt Romney never knew how to win. He is a pompous 'ass' who has been fighting me from the beginning, except when he begged me for my endorsement for his Senate run (I gave it to him), and when he begged me to be Secretary of State (I didn’t give it to him). He is so bad for R’s!" Trump added in another tweet.

Somebody please wake up Mitt Romney and tell him that my conversation with the Ukrainian President was a congenial and very appropriate one, and my statement on China pertained to corruption, not politics. If Mitt worked this hard on Obama, he could have won. Sadly, he choked! — Donald J. Trump (@realDonaldTrump) October 5, 2019

Mitt Romney never knew how to win. He is a pompous “ass” who has been fighting me from the beginning, except when he begged me for my endorsement for his Senate run (I gave it to him), and when he begged me to be Secretary of State (I didn’t give it to him). He is so bad for R’s! — Donald J. Trump (@realDonaldTrump) October 5, 2019

A spokesperson for Romney did not immediately return a request for comment Saturday.

Romney, who has at times been a vocal critic of Trump's policies and actions in office, broke sharply this week with Trump's call for China and Ukraine to investigate Biden, a leading Democratic presidential contender. Romney called the effort "wrong and appalling."

"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 Friday.

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

GOP Sen. Ben Sasse Benjamin (Ben) Eric SasseWhy a backdoor to encrypted data is detrimental to cybersecurity and data integrity McEnany says Trump will accept result of 'free and fair election' McConnell pushes back on Trump: 'There will be an orderly transition' MORE (Neb.) this week also broke with Trump's suggestion that China should investigate Biden, saying in a statement to a local newspaper that "Americans don't look to Chinese commies for the truth. If the Biden kid broke laws by selling his name to Beijing, that's a matter for American courts, not communist tyrants running torture camps."

Details of Trump's July 25 call with the Ukrainian president, in which he pushed the foreign leader to investigate Biden and unproven allegations of corruption involving the former vice president and his son, are at the center of House Democrats' impeachment inquiry against Trump.

Romney has voiced concerns about Trump's comments during the call since reports about the conversation began to emerge last month. The GOP senator called a rough transcript of the call released by the White House last week "deeply troubling."

The reconstituted transcript showed Trump asking the Ukrainian leader to "look into" his allegations surrounding Biden and to work with his personal attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE on the matter.

Updated: 11:05 a.m.