Sen. Mitt Romney is one of the first Republicans to speak out against President Trump's call to Ukraine to investigate former Vice President and Democratic presidential candidate Joe Biden.

In a tweet, Romney condemned the action.

“If the President asked or pressured Ukraine’s president to investigate his political rival, either directly or through his personal attorney, it would be troubling in the extreme," he wrote. "Critical for the facts to come out." 

Romney's tweet comes amid reports that Trump and his attorney Rudy Guiliani tried to persuade Ukrainian president  Volodymyr Zelenskiy to open an investigation against Biden.

Trump said Sunday that he spoke to Ukraine's new president about his summer election and the fact that "we don't want our people, like Vice President Biden and his son" contributing to corruption already happening in the Eastern European nation. He stopped short of acknowledging whether or not he explicitly asked Zelensky to investigate Biden on the July 25 phone call  that is the subject of an anonymous whistleblower report. 

The White House has not yet released a transcript of the call. 

Trump's administration plunged into an extraordinary showdown with Congress Thursday over access to a whistleblower's complaint. The blocked complaint is both "serious" and "urgent," the government's intelligence watchdog said.

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The administration kept Congress from even learning what exactly the whistleblower is alleging, but the intelligence community's inspector general said the matter involves the "most significant" responsibilities of intelligence leadership. A lawmaker said the complaint was "based on a series of events."

House Speaker Nancy Pelosi penned a letter to members of Congress, saying that "if the Administration persists in blocking this whistleblower from disclosing to Congress a serious possible breach of constitutional duties by the president, they will be entering a grave new chapter of lawlessness which will take us into a whole new stage of investigation.”