The Senate Interactive Map has been updated with the Georgia special election. The initial consensus rating is Leans Republican.
The added Georgia election will be for the final two years of Sen. Johnny Isakson's term. Isakson recently announced his resignation, effective at the end of this year. Gov. Brian Kemp will select a replacement who will serve until the winner of the special election takes office in January, 2021.
There are now 35 Senate seats to be contested^ in 2020, 23 held by Republicans, 12 by Democrats. The GOP holds a 53-47 edge. Democrats must have a net gain 3 or 4 seats to take control, depending on the outcome of the presidential election*.
Sabato's Crystal Ball and Inside Elections have started the special election with a Leans Republican rating, while The Cook Political Report has gone with Likely Republican. These ratings all mirror those that each forecaster has in place for Georgia's other U.S. Senate seat, which will be up for a regular six-year term in 2020. This makes sense, at least until we have a better handle on who is running, as these 'double-barrel' Senate races usually break the same way. The last time the parties split in this kind of situation was 1966.
A couple other things to keep in mind...
The Georgia special election will be a 'jungle primary' where all candidates will appear on a single ballot. There will be no party primaries prior to this.
Georgia requires a runoff if no candidate gets a majority of the vote. If either or both of these races need a runoff, it won't take place until January 5, 2021. That is after the expected start of the 117th Congress on January 3, 2021. The November elections could play out in such a way that we won't know who will ultimately control the Senate until January.
^ The Arizona race is also a special election. The winner will complete the final two years of the term of the late John McCain. Gov. Doug Ducey initially appointed Jon Kyl to the role. Kyl later resigned, and Sen. Martha McSally was appointed to replace him.
* A 3 seat net Democratic gain would tie the Senate at 50-50. The vice president breaks ties, so if this were to the result of the 2020 election, control would go to the party that wins the presidency. There is a VP box on the Senate Interactive Map where you can make this selection.