While the party will be on defense in every competitive race, Republicans face some messy primaries and a recent history of nominating extreme candidates who have lost key contests.
Ruben Gallego, a Democratic congressman vying for one of the most competitive Senate seats in the country, is pitching himself to Native American voters.
Kyrsten Sinema, the independent incumbent, has not announced whether she will run for re-election. But as both parties in Arizona prepare for that outcome, Republicans are worried.