Democrats have a razor-thin 51-49 majority Democrats risk losing the Senate this year, as incumbents in the Montana and Ohio Senate races face an uphill climb—and the party fights for Arizona and Pennsylvania.

The Montana Supreme Court on Tuesday affirmed a lower court ruling which allowed the state’s Green Party Senate candidate to remain on the ballot in November, a blow to Democrats’ efforts to prevent what they expect could be a spoiler in the close race between incumbent Sen.