At FiveThirtyEight, we’ve been projecting the probability (56.9 percent in the current Senate forecast) that Republicans will have at least 51 seats in the 114th Congress. But chances are they will not have won at least 51 seats on Election Day, Nov. 4, or even by the end of the month.

The reason? Two states, Louisiana and Georgia, will hold runoffs if no Senate candidate receives greater than 50 percent of the vote on Nov. 4. Republicans are about a 3-to-1 favorite in those states, and winning both is part of the GOP’s easiest path to a chamber majority.

Polls have consistently indicated that Republican Rob Maness will keep Republican Bill Cassidy and Democratic Sen. Mary Landrieu both under 50 percent in Louisiana’s jungle primary. That would force a runoff between Cassidy and Landrieu on Dec. 6.

If Landrieu retains her seat in the Pelican State, it’s possible the GOP will get 51 seats by claiming victories in places where it has at least a 60 percent of winning (according to the FiveThirtyEight forecast), as well as in two of the following states: Colorado, Iowa and Kansas. That isn’t likely at this point, but it’s more than conceivable.

But the more intriguing scenario involves Georgia, which would hold a runoff Jan. 6. That’s right. Georgia’s runoff would occur after Congress is sworn in on Jan. 3.

What’s the chance of a runoff there? It seems to be higher by the day. A SurveyUSA poll out Wednesday gives Republican David Perdue just a 46 percent to 45 percent lead over Democrat Michelle Nunn. The FiveThirtyEight forecast is a bit more optimistic for Perdue, projecting him to lead the November vote by 3.2 percentage points. You’ll note I’m hesitant to say “win.” The reason is that the Libertarian candidate, Amanda Swafford, has averaged 5 percent in the past five polls to include her as a choice. The SurveyUSA poll put her at 4 percent. It’s impossible for Perdue to beat Nunn by 3 percentage points in November and get over 50 percent if Swafford earns 4 percent of the vote.

In other words, if Nunn and Perdue are close, and Swafford does decently, Georgia is headed for a runoff.

And there’s precedent for such a performance by a Libertarian. In Georgia’s 2008 Senate race, Libertarian Allen Buckley won 3.4 percent of the vote. That was enough to keep Republican Sen. Saxby Chambliss, who led the November vote by 3 percentage points over Democrat Jim Martin, at 49.8 percent of the vote.

However, third-party candidacies often fade. FiveThirtyEight’s model has Swafford winning just 2.5 percent of the vote in November and Perdue barely topping 50 percent. That doesn’t leave a lot of room for Perdue; he could easily fall below 50 percent in later projections and force a January runoff, in which he would be favored, yet not guaranteed, to win.

If there’s a runoff, Republicans would probably need to win Colorado, Iowa and Kansas for Georgia not to determine the majority. That’s possible but unlikely.

A lot of angry political reporters may be spending their New Year’s celebration in Georgia.