Analysis: The biggest obstacle Republicans face in the battle for the Senate

Greitens, who quickly faced calls from Senate Republicans and his GOP primary opponents to exit the race, has denied the allegations. Missouri is a solidly red state, but some Republicans fear that Greitens, who had been viewed as the front-runner in the primary, could single-handedly put it in play if he advanced to the general election.

There’s also been a lack of clarity in Republican Senate primaries in more traditional battleground states. In Ohio, the race has become more combative — literally — in recent days, with candidates Josh Mandel and Mike Gibbons getting in each other’s faces during a debate.

In Pennsylvania — where the candidate former President Donald Trump endorsed, Sean Parnell, suspended his campaign last November — leading candidates Mehmet Oz and David McCormick have been upping their attacks on each other. Most recently, McCormick called Oz’s Turkish citizenship — which he said he would renounce if elected — into question.

In North Carolina, the Trump-endorsed Ted Budd hasn’t vaulted to the front of the primary pack as expected, Budd was the target of a recent ad from GOP rival Pat McCrory accusing him of being “friendly” toward Russia. (In the much safer Republican state of Alabama, Mo Brooks, another Trump-backed candidate, is also lagging.)

And in Arizona and New Hampshire, Republicans are left without their top recruits after Govs. Doug Ducey and Chris Sununu passed on Senate bids.

Now, even for the primaries coming up in May, there’s still a long way to go, as more GOP voters start to tune in. Trump could still tip the scales in states like Missouri, Ohio and Pennsylvania with endorsements. Even the nastiest primary fights don’t necessarily preclude the party from rallying together in November. And a favorable political environment on its own could solve many of the GOP’s problems.

But Republicans also know all too well that settling on the wrong nominee (see: Christine O’Donnell, Todd Akin, Roy Moore) can cost a party otherwise winnable seats. Given the evenly divided Senate, and that the most competitive races are set to take place in states President Joe Biden carried in 2020, there won’t be a massive margin for error for the GOP.

The Point: Between Biden’s low approval ratings and the historical nature of midterm elections, Republicans have plenty working in their favor in their effort to win the Senate majority. But they also can’t afford many self-inflicted wounds.