|Senate Democrats*||Senate Republicans|
|11.4% probability of a majority||88.6% probability of a majority|
|Mean of 48 seats||Mean of 52 seats|
Control of the Senate is up for grabs this fall. My previous analysis showed Democrats with a average of 49 seats and Republicans with 51 seats, putting the Democrats in range to flip the Senate. That was over a half year ago, so it is time to update the analysis using a plethora of new polls released since then.
After 100,000 simulated elections, Democrats have a Senate majority 1,914 times, (and there were 9,521 ties), and Republicans control the Senate 88,565 times. If the election was now, Democrats would have an 11.4% probability of controlling the Senate and Republicans an 88.6% probability of controlling the Senate. Of course, if Republicans end up in the White House, the ties would go to them.
Here is the distribution of Senate seats from the simulations:*
The most likely outcome is a 52 to 48 split with Republicans in charge. Here are some state-by-state comments.
Florida: Without question, the return of Marco Rubio to the Senate race has changed the likely outcome. Democrat Patrick Murphy has a fight on his hands. Polls occasionally favor Murphy, but the most likely outcome is a victory for Rubio (assuming they both come out on top in the August 30 primary).
Republican Mark Kirk leads Democrat Tammy Duckworth in the only recent poll. Up ’till now, Kirk has been considered one of the most endangered Republican incumbents. Duckworth crushed Kirk a year ago, and then there was a long poll-less period. Clearly more Illinois polls are needed.
Nevada: Harry Reid’s (D) seat is up for grabs with Catherine Cortez Masto (D) besting Joe Heck (R) based on two recent polls. Cortez Mastro only has a 67% probability of taking the seat based on these polls. Most older polls show Heck with the advantage. This one is a toss-up.
New Hampshire: Sen. Kelly Ayotte (R) is facing a mighty challenge from Governor Maggie Hassan (D). The six current polls give the Democrat a slim 54% probability of taking the seat. This is, essentially, a tie, and the polling history shows this to be an extremely close race with a small advantage to Ayotte.
Ohio: Sen. Rob Portman (R) has pulled ahead of former Gov. Ted Strickland (D), after Strickland led for most of the past year. Portman would win an election now with a 91.9% probablity.
Wisconsin: Sen. Ron Johnson (R) is the most endangered sitting Senator in the country. He is likely to lose to former Sen. Russ Feingold (D), if the polling to date is any indication.
This graphs shows the probability of at least each number of seats controlled by the Democrats:*
- 100000 simulations: Democrats control the Senate 11.4%, Republicans control the Senate 88.6%.
- Average ( SE) seats for Democrats: 48.2 ( 1.1)
- Average (SE) seats for Republicans: 51.8 ( 1.1)
- Median (95% CI) seats for Democrats: 48 (46, 50)
- Median (95% CI) seats for Republicans: 52 (50, 54)
Expected outcomes from the simulations:
- Democratic seats w/no election: 35
- Independent seats w/no election: one
- Republican seats w/no election: 30
- Contested Democratic seats likely to remain Democratic: ten
- Contested Republican seats likely to remain Republican: 22
- Contested Democratic seats likely to switch: none
- Contested Republican seats likely to switch: two
This table shows the number of Senate seats controlled for different criteria for the probability of winning a state:* Safe>0.9999, Strong>90%, Leans>60%, Weak>50%
|Threshold||Safe||+ Strong||+ Leans||+ Weak|
This table summarizes the results by state. Click on the poll number to see the individual polls included for a state.
|State||@||polls||size||Democrat||Republican||% wins||% wins|
@ Current party in office
& An older poll was used (i.e. no recent polls exist).
*Analyses assume that the two independent candidates will caucus with the Democrats.
Details of the methods are given in the FAQ.