Susan Collins is up for reelection in a state that Hillary Clinton carried in 2016. And although there’s nothing to prove it yet in the polling, this race could be very different than the last four, in which she easily swept her Democratic opponents.

Moderation has been Collins’ greatest strength each time. She appeals to voters in both political parties who value thoughtfulness and middle ground. But it’s that very thing that has turned left-leaning voters against her.