Susan Collins

A new accusation that Graham Platner once sexually assaulted a woman he was dating has rocked the U.S. Senate race in Maine and cast fresh doubt on Democrats’ path to a Senate majority.

Republicans currently have a 53-47 advantage in the Senate, and Maine is viewed as a necessary win for Democrats to gain the minimum of four new Senate seats.

But now there’s a question of whether Platner, who denied the allegation, will remain on the ballot and, if he does, whether he can defeat five-term Republican Sen. Susan Collins.

Here’s a closer look at the top races that Democrats are targeting.