Sen. Susan Collins (R-Maine) said on Saturday it was "completely inappropriate" for President Trump to urge China to investigate former Vice President Joe Biden and his son Hunter Biden.

"I thought the president made a big mistake by asking China to get involved in investigating a political opponent. ... It's completely inappropriate," Collins told the Bangor Daily News.

Collins's comments came after Trump suggested to reporters outside the White House on Thursday that China and Ukraine should investigate the Bidens.

"China should start an investigation into the Bidens," Trump said in front of cameras on the South Lawn.

The president added that he had not explicitly asked Chinese President Xi Jinping to open such a probe but that it's "certainly something we can start thinking about."

Collins - who is up for reelection in a state won by Hillary Clinton in 2016 - is one of the few Republican senators who have publicly pushed back against Trump's comments. Most have remained silent as they are dispersed across the country and in the middle of a two-week recess.

Sen. Ben Sasse (R-Neb.) said in a statement on Thursday night that "Americans don't look to Chinese commies for the truth" but also knocked House Intelligence Committee Chairman Adam Schiff (D-Calif.) for running a "partisan clown show in the House."

Sen. Mitt Romney (R-Utah) pushed back forcefully on Thursday, calling Trump's rhetoric "wrong and appalling" and saying it "strains credulity to suggest that it is anything other than politically motivated."

Underscoring the risk for GOP senators who speak out against Trump, the president has spent the weekend lashing out at Romney, including calling him a "pompous 'ass'" and calling for his impeachment.

Trump's suggestion that China should investigate the Bidens comes as House Democrats are at the start of an impeachment inquiry centered on allegations that Trump sought to withhold aid to Ukraine in an effort to get Kiev to launch a probe.

Collins told the Maine publication that she had concerns that Schiff "misrepresented and misled people about what was in the transcript in the call," an apparent reference to the summary Schiff offered during a public hearing.

Schiff's portrayal has earned fierce criticism from Republicans, who are expected to force a vote on a resolution to censure him. Schiff said that his summary of Trump's phone call with the Ukraine President Volodymyr Zelensky was supposed to be partly a parody.

No Senate Republican has backed an impeachment inquiry against the president, with several suggesting they think House Democrats are overplaying their hand.

Collins has previously declined to comment on impeachment and reiterated her position to the Bangor Daily News on Saturday.

"Should the articles of impeachment come to the Senate - and right now I'm going to guess that they will - I will be acting as a juror as I did in the Clinton impeachment trial," Collins said.