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 (R-Utah) on Thursday brushed off the latest round of criticism against him from 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.

"First of all, I don't follow the president on Twitter so I don't see all of his tweets. But secondly, you know, in my business, if you got concerned about criticism, you'd be in the wrong business. So I just don't worry about those things," Romney told reporters in Utah.

When a reporter began to bring up Trump's comments, Romney quipped: "Oh, don't repeat them."

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Trump has lashed out at Romney in recent weeks after the GOP senator raised concerns about the president's July 25 phone call in which he asked Ukrainian President Volodymyr Zelensky to "look into" 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 and his son, Hunter Biden.

Romney also spoke out late last week after Trump publicly urged China and Ukraine to investigate the Bidens, calling the president's comments "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 said on Friday.

Trump quickly hit back, calling Romney a "pompous ass" and suggesting he should be impeached.

"I’m hearing that the Great People of Utah are considering their vote for their Pompous Senator, Mitt Romney, to be a big mistake. I agree! He is a fool who is playing right into the hands of the Do Nothing Democrats! #IMPEACHMITTROMNEY," Trump tweeted.

Romney, a former governor of Massachusetts, joined the Senate in January and has quickly emerged as one of the president's most vocal critics within the GOP caucus. According to FiveThirtyEight, however, Romney has voted with Trump nearly 80 percent of the time.

He initially drew criticism from Trump last month after he called the White House’s partial transcript of the Trump-Ukraine call "deeply troubling."

Asked on Thursday why he was one of a few GOP senators speaking out publicly, Romney indicated that unhappiness within the caucus over Trump's remarks was privately more widespread.

"I think everyone understands that asking a foreign government to investigate one’s political opponent is wrong. I don't think there's any exception to that. People might try to stay silent," he said.

"But there's no question that on its face asking China to investigate Mr. Biden, asking Ukraine, is simply the wrong thing to do," Romney added.

House Democrats are at the start of an impeachment inquiry centered on Trump's dealings with Ukraine, including his request that the Ukrainian government work with the president's personal lawyer, 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, to investigate the Bidens. They are also probing allegations that the president tried to withhold aid to Ukraine in an effort to get Kiev to launch such a probe.

No Republican senator has backed the House impeachment inquiry or removing Trump from office.

Romney on Thursday declined to weigh in on either, saying he would wait to make a decision after the House sent articles of impeachment to the Senate, which would kick off a trial.

"That's something which I would have to consider down the road," he said.

Asked if he had privately already made a decision, he added, "I'll keep an open mind until and unless there is some kind of decision reached by the House. ... It's a purposeful effort on my part to stay unbiased, and to see the evidence as it's brought forward."