Fourth, the animosity between Republican leaders and grassroots activists is worsening. The feud between Senate Majority Leader Mitch McConnell and former Trump adviser Steve Bannon has gotten so bad that it threatens to dampen Republican turnout—at a time when the Democrats’ own engagement is supercharged. These divisions hamper the party’s ability to nominate an electable successor to Sen. Jeff Flake of Arizona, who was forced to retire because he alienated the pro-Trump wing of the GOP. Party leaders also fear that a deeply flawed candidate could threaten a senator in a primary—and put an otherwise safe seat in play for the Democrat.

Senate Republicans have gone from dreaming of a Senate supermajority to merely hoping to prevent any losses for 2018. The favorable map is likely to protect them from losing the majority, but their margin for error will be narrow. Republicans still have promising opportunities in Missouri and Indiana, but they face a serious risk of losing seats in Arizona and Nevada. There are other opportunities for Republicans, but they look less encouraging than they once did. As things stand now, netting any seats would count as a victory.