Final forecast: Dems have three-in-four chance of flipping Senate

First, there are the two Republican-held seats most likely to fall to Democrats: Colorado and Arizona. In Colorado, former Gov. John Hickenlooper’s chances of defeating Republican Sen. Cory Gardner look particularly strong: 84 in 100. This is probably due in part to the fact that Joe Biden looks extremely likely to carry Colorado, and it’s become increasingly rare for voters to split their tickets between the presidential and Senate races. In Arizona, Biden’s victory is less assured, but former astronaut Mark Kelly has proven to be an extremely strong recruit for Democrats in Arizona, raising more than $87 million in individual contributions and leading in almost every poll since he entered the race in early 2019. Hurt by the fact that she is an appointed senator (which affords her almost no incumbency advantage), Republican Martha McSally has just a 22 in 100 chance to prevail.

Two additional Republican-held seats lean toward Democrats — although in all likelihood, we’ll only know who won one of them today: North Carolina. There, former state Sen. Cal Cunningham is a 68 in 100 favorite to defeat Republican Sen. Thom Tillis. Despite revelations that Cunningham sent sexts to a woman who is not his wife, the race has been pretty stable, and he has managed to hold onto a narrow polling lead. We give Democrats similar odds (a 63 in 100 chance) of eventually prevailing in Georgia’s special election — but this race will almost certainly not be decided until January. That’s because the race is a battle royal among 20 candidates of all parties (there was no primary), making it nearly impossible that any one candidate will secure the majority of votes necessary to win. Assuming that doesn’t happen, the top two finishers will advance to a runoff on Jan. 5. Democrats currently lead in polls of the runoff, but a lot can happen in the next two months, and Georgia remains a Republican-leaning state.