(CNN) Several Senate Republicans, who have been at odds with President Donald Trump, won't say if they'd consider backing his new primary opponent, Bill Weld.

Utah Sen. Mitt Romney, like Weld, was once governor of Massachusetts and has been openly critical of Trump at times during his presidency. But a Romney spokeswoman declined to comment Tuesday when asked if the freshman Republican would be open to backing Weld over Trump.

Similarly, Sen. Susan Collins, the Maine Republican who is up for re-election in 2020 and did not back Trump in 2016, would not say earlier this year if she would support Trump's bid for a second term. And on Tuesday, a spokesperson did not respond to multiple inquiries seeking comment about her view on Weld's primary bid.

Other GOP senators, too, who have sparred with Trump in the past were mum when asked by CNN on Tuesday about Weld's new campaign, including Sen. Ben Sasse of Nebraska, whose spokesman didn't respond to multiple emails about whether his boss is open to Weld.

Two of the more vulnerable Senate Republicans up in 2020 also were quiet on Tuesday. A spokesperson for Sen. Thom Tillis, the North Carolina Republican, did not respond to multiple requests for comment about Weld's candidacy, while Arizona Sen. Martha McSally, who faces a difficult election bid in 2020, declined to comment through a spokesperson.

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