“I thought the president made a big mistake by asking China to get involved in investigating a political opponent,” she said.
Although Ms Collins did not say if she would support the removal of Mr Trump from office, she said she hoped the impeachment process “will be done with the seriousness that any impeachment proceeding deserves.”
An impeachment inquiry would need to pass the House of Representatives before Mr Trump can be removed from office by the Senate.
However, a two-thirds supermajority vote is needed to convict the president in the Senate, where the Republican Party currently has a majority and its leadership is unsupportive of an impeachment inquiry.
Earlier this week, Mr Romney said Mr Trump’s appeal to China and Ukraine was “wrong and appalling”.
In a statement to the Omaha World-Herald newspaper, Mr Sasse did not explicitly name the president but echoed Mr Romney's condemnation.
“Hold up: Americans don’t look to Chinese commies for the truth,” he wrote.
“If the Biden kid broke laws by selling his name to Beijing, that’s a matter for American courts, not communist tyrants running torture camps.”
Mr Trump and his personal lawyer, Rudy Giuliani, have been attempting to draw attention to the business dealings of Hunter Biden, the former vice president’s son, by alleging without evidence that he has been involved in corruption.
Geng Shuang, a spokesperson for China’s foreign ministry, described the allegations against the Bidens as “totally groundless” on Monday.
In Ukraine, the country’s top prosecutor Ruslan Ryaboshapka said he was not aware of any evidence of wrongdoing by the Bidens.
However, Mr Ryaboshapka added he is reviewing several cases related to the owner of Burisma, an energy company where Hunter Biden served as a board member.
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