Story highlights Collins said there will likely be a Senate Ethics Committee investigation into Moore if he wins

Moore has vowed to win in the face of the "Washington establishment"

Washington (CNN) Sen. Susan Collins, R-Maine, said Thursday that Senate Republicans will have little choice but to seat Alabama Senate hopeful Roy Moore if he wins next month.

"If he is elected, there are no grounds under the Constitution to fail to seat him," Collins said at a breakfast held by The Christian Science Monitor. "The Constitution says you can only look at citizenship, whether they are a resident of the state, and if they are the proper age. So we have to seat him."

Moore's campaign was rocked earlier this month by allegations that he pursued relationships with teenage girls while in his 30s, including accusations of sexual assault. He has denied all the allegations.

Several Republicans have come out against Moore's candidacy, and Sen. Cory Gardner, R-Colorado, the head of the National Republican Senatorial Committee, said if Moore wins, the Republican-controlled Senate should vote to expel him.

Collins, who noted Thursday that she supported Sen. Luther Strange, Moore's opponent, in the Alabama Republican Senate primary, said she will take her cues from a Senate Ethics Committee investigation that she believes will be set up if Moore wins.

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