Maine Sen. Susan Collins addresses reporters outside the Firefighters Memorial in Capitol Park. Collins called it "completely inappropriate" that President Trump made a public request for a foreign leader, China, to investigate his political foe. Credit: Nick Schroeder | BDN

AUGUSTA, Maine — U.S. Sen. Susan Collins, R-Maine, joined two other GOP senators in criticizing the president this week after he publicly asked the Chinese government to investigate a political opponent while talking to reporters outside the White House this week.

The Maine senator was unequivocal in her statements, which came after a firefighters memorial service in Augusta on Saturday morning, joining Mitt Romney, R-Utah, and Ben Sasse, R-Nebraska, in breaking rank with GOP support for the president.

“I thought the president made a big mistake by asking China to get involved in investigating a political opponent,” Collins said. “It’s completely inappropriate.”

The president’s comments came days after House Speaker Nancy Pelosi, D-California, announced a formal impeachment probe into his attempt to solicit foreign help in an election, which is illegal and considered by many lawmakers to be a foundational threat to democracy.

Collins reiterated that she would not offer comment on the evidence, saying that not all of it is in yet, and that she hopes the impeachment process “will be done with the seriousness that any impeachment proceeding deserves.”

An impeachment probe would need to pass the House before it reaches Collins’ review, which is expected to do. House Democrats have issued subpoenas to the White House, including Secretary of State Mike Pompeo, and are in the process of gathering witnesses and evidence.

“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.

Collins also said that she was concerned that U.S. Rep. Adam Schiff, D-California, chair of the House Intelligence Committee, “misrepresented and misled people about what was in the transcript in the call,” joining Republican efforts to discredit the congressman.

A September whistleblower complaint uncovered a phone call the president made to newly elected Ukraine President Volodymyr Zelensky, in which Trump appeared to pressure the foreign leader to investigate Democratic presidential candidate Joe Biden, his potential opponent in the 2020 election, while the U.S. was withholding $250 million in foreign aid to Ukraine for reasons unclear to that country’s government.

Along with his personal lawyer, Rudy Giuliani, the president has without evidence been attempting to drum up public scrutiny about the business dealings of Hunter Biden, the former vice president’s son, in Ukraine and China. Trump has called his phone call to Ukraine “perfect,” and said that he has an “absolute right” to ask foreign leaders to investigate corruption cases.

On Monday, Geng Shuang, a spokesman for China’s Ministry of Foreign Affairs, called the allegation that Chinese government business gave Biden’s son $1.5 billion “totally groundless.”

On Friday, Ukraine’s top prosecutor said he was looking into several cases related to the Bidens’ business dealings in the country, adding that he was not aware of any wrongdoing from either Biden.

Watch: Susan Collins slams Adam Schiff over Ukraine probe