Sen. Mitt Romney of Utah became one of the first congressional Republicans on Sunday to call for more information about President Donald Trump s alleged efforts to get Ukraine to investigate former Vice President Joe Biden .

If the President asked or pressured Ukraines president to investigate his political rival, either directly or through his personal attorney, it would be troubling in the extreme Romney tweeted. Critical for the facts to come out.

The House Intelligence Committee is investigating a whistleblower complaint filed last month that reportedly accuses Trump of repeatedly pressuring Ukraine President Volodymyr Zelensky to investigate the former vice president, who is currently running for president.

Trump claims Biden called for the removal of a notoriously corrupt prosecutor in Ukraine to hamper an investigation into a Ukranian gas company, where his son Hunter served on the board of directors. Ukrainian authorities have said theres no evidence to suggest any wrongdoing by Biden.

The complaint was deemed credible and of urgent concern by Michael Atkinson, the inspector general for the U.S. intelligence community. But Acting Director of National Intelligence Joseph Maguire, whom Trump appointed last month, has so far refused to share the complaint with Congress.

The explosive allegations, which, if true, could amount to a U.S. president seeking assistance from a foreign government to help his reelection campaign, have reignited calls for impeachment from many Democrats .

House Speaker Nancy Pelosi (D-Calif.), who has been reluctant to open an impeachment inquiry against Trump to the ire of her progressive colleagues, warned Sunday that efforts by the Trump administration to block Congress from seeing the complaint would lead to a whole new stage of investigation.

But Republicans have largely defended the president in the wake of the allegations. Sen. John Cornyn (R-Tex.) told reporters Sunday theres no direct evidence that Trump asked Zelensky to investigate Biden.

Trump, however, has acknowledged that he discussed Biden during the July phone call with Zelensky. His personal attorney, Rudy Giuliani, told The Washington Post on Sunday that he doesnt do anything that involves my client without speaking with my client when asked if Trump approved Giulianis requests that Ukrainian officials investigate Biden.

Sen. Pat Toomey (R-Penn.) told NBC on Sunday that he doesnt know the context of Trumps call with Zelensky, but said its not appropriate for any candidate to ask for assistance from a foreign government.

Trump claimed his conversation with Zelensky was perfect but said he would consider releasing a transcript of the call, which Biden has urged him to do.

Its unclear what actions Romney believes should be undertaken to ascertain the full facts of Trumps dealings with Ukraine.

A representative for Romney did not immediately respond to HuffPosts request for comment.