Conservative and Tea Party backed-State Sen. Chris McDaniel appears to be leading the establishment incumbent U.S. Sen. Thad Cocrhan in polls of Republican voters by six poiints and also appears to have the momentum. But there is no guarantee that only Republicans will vote in the runoff on Tuesday, June, 24. The reason is the odd election law in Mississippi does allow Democrats to vote in the GOP nomination runoff race as long as they did not vote in the Democratic primary on June 3rd.
The only registered voters prohibited from voting Tuesday are those who voted in the Democratic primary June 3, according to the Mississippi Secretary of State's office.
Those who voted in the Republican primary can vote. Those who did not vote at all on June 3 can vote.
This system has been the source of litigation and frequent arguments in favor of changing the law. Tea party groups have hired an elections attorney to monitor the election day machinery because they say "the potential for abuse and illegality is obviously huge."
The net impact for Tuesday is that unless a voter voted Democratic on June 3, a voter can still vote in the Republican runoff. I think it is a very stupid law but that is the law in place for June 24.
The final wrinkle to consider is this. There are some Democrats who support Sen. McDaniel for different reasons. Even if a Democrat wants to vote in the GOP runoff, there is no certainty that the Democrat will vote for Cochran instead of McDaniel. Some Democrats might think Cochran is the more liberal candidate but they also might think they would prefer to defeat Cochran if that made it easier to elect a Democrat in the fall. But since Mississippi is a strong Republican state right now, many voters in the state see the runoff on Tuesday as tantamount to the final November election. Former Sen. Rick Santorum, who won the Mississippi presidential primary over Mitt Romney and Newt Gingrich in 2012, has been campaigning with State Sen. McDaniel in events featuring the Tea Party Express bus and incumbent Sen. Thad Cochran has been campaigning with Sen. John McCain (R-Ariz.) and retired Green Bay Packers quaterback Bret Favre who is from Mississippi.