Last week, Mississippi Sen. Thad Cochran announced that he was resigning due to health issues, triggering a November special election for the open Senate seat. Mississippi isn’t usually a problematic state for Republicans. It’s a strongly red, highly inelastic state—meaning that it usually votes for GOP candidates by a solid, reliable margin, regardless of which way the political winds are blowing.

But if Mississippi Republicans catch multiple successive unlucky breaks, this seat could become a problem for them. On Wednesday, Chris McDaniel might have hit the GOP with that first unlucky break.

In order to understand exactly what McDaniel did and why it matters, we have to rewind a bit. Before Cochran decided to retire, McDaniel attempted to primary Mississippi’s other senator, Roger Wicker. Wicker is up for re-election in 2018, and he seemed like a safe bet to win the general election. But McDaniel has shown some strength with the statewide GOP: He almost beat Cochran in the 2014 Republican Senate primary. And some Republicans feared—both in 2014 and 2018—that if McDaniel, a candidate with real baggage, were to win the nomination, he could allow Democrats to take an ordinarily safe Senate seat.

And on Wednesday, McDaniel announced that he would run for Cochran’s open seat rather than challenge Wicker from the right. McDaniel’s decision makes sense. Senate seats don’t open up every day, and he probably (I think correctly) calculated that he has a better chance of winning Cochran’s seat than he does of beating Wicker.

But McDaniel’s candidacy could create problems for Republicans. Mississippi’s special election rules are a little wonky: All of the candidates will run in a nonpartisan primary in November. If no candidate gets above 50 percent of the vote, the top two candidates advance to a run-off election. Mississippi is flush with Republicans: There are qualified statewide office holders, former statewide office holders, state legislators, and more who could credibly run. If Gov. Phil Bryant's appointee to the seat (he gets to appoint a temporary replacement for Cochran who will likely run) fails to keep other candidates out of the race, the non-McDaniel Republicans could split the vote while McDaniel keeps enough of his core constituents to make it to the run-off.

If Democrats manage to take advantage of the highly Democratic national environment, get a strong candidate into the run-off, capitalize on McDaniel’s weaknesses, grab some Republican votes, and maintain a turnout advantage, they could take the seat.

This scenario shouldn’t sound likely. It should feel a bit like a big domino line: If one piece is out of place (e.g. a weak Democratic candidate, a strong GOP consensus alternative to McDaniel emerges, McDaniel scores a typical Republican win in the run-off despite his disadvantages, etc.), it could stop the succession of events that would lead to a Democratic win in Mississippi.

But it’s worth thinking about these possibilities. Only a few months ago, Republican Roy Moore lost a Senate race to Democrat Doug Jones. Obviously McDaniel isn’t Moore. Moore was credibly accused of having improper sexual contact with teenage girls while he was in his 30s, making him a uniquely terrible candidate. But McDaniel might still underperform a more generic Republican and give Democrats a shot at the seat.

All things considered, this race is still a likely Republican hold. It’ll be hard to make further judgments until we know more about the field and see some polling. But it’s worth watching these developments now, because stranger things than a Republican loss in Mississippi have happened—like a Republican loss in Alabama.