Election 2020: Senate Races

Senate Democrats*	Senate Republicans
greater than 99.9% probability	less than 0.1% probability
Mean of 54 seats	Mean of 46 seats

My previous analysis, just over a week ago, showed control of the Senate going to Democrats with, on average, 53 seats going to the Democrats and 47 seats going to the Republicans. After 100,000 simulated elections, Democrats won 97,022 of them, Republicans only won 42 times and there were 2,936 ties. Since then, about 38 new polls have been released.

Today, after 100,000 simulated elections, Democrats have a Senate majority 99,919 times, Republicans control the Senate 21 times, and there were 60 ties. In other words, the results for Democrats have improved a bit, with the average number of seats going up by one to 54. Democrats would almost certainly take control of the Senate if the race was held today.

This week, we got the first polls in several races, including Tennessee, Oregon, Massachusetts, and the Georgia-2 special election. In fact, that poll is largely responsible for the one-seat bump from last week. Georgia’s special election has no primary. Instead numerous candidates will be on the ballot on November 3rd, and a runoff election will be held in the almost certain event that no one candidate takes 50% of the vote. The Civiqs poll conducted heat-to-head contests between different combinations of candidates. At this point it looks like the runoff is between Democrat Raphael Warnock and Republican Senator Kelly Loeffler, who holds the seat by appointment. The poll puts Warnock up over Loeffler 49% to 39%. Of course, this is only one poll, and an unconventional one at that, but it has totally changed my perception of this race, which I assumed would go to the incumbent Republican.

Democrats make progress in several other races, as well, including the GA-1 Senate race (from 16% probability last week to 33% probability of winning the state in an election held today), Iowa (45% to 70%) and Montana (30% to 43%). Republicans gained in Kansas (from 50% to 82%). I should note that only a few of the twenty North Carolina polls were taken (or partially taken) after Democrat Cal Cunningham’s “sexting” scandal broke. We’ll need more polls to see how that race develops.

Here is the distribution of Senate seats from the simulations:^*

This graphs shows the probability of at least each number of seats controlled by the Democrats:^*

• 100000 simulations: Democrats control the Senate 100.0%, Republicans control the Senate 0.0%.
• Average ( SE) seats for Democrats: 54.0 ( 1.3)
• Average (SE) seats for Republicans: 46.0 ( 1.3)
• Median (95% CI) seats for Democrats: 54 (52, 56)
• Median (95% CI) seats for Republicans: 46 (44, 48)

Expected outcomes from the simulations:

• Democratic seats w/no election: 34
• Independent seats w/no election: one
• Republican seats w/no election: 30
• Contested Democratic seats likely to remain Democratic: 11
• Contested Republican seats likely to remain Republican: 17
• Contested Democratic seats likely to switch: one
• Contested Republican seats likely to switch: six

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
Safe Democrat	44
Strong Democrat	7	51
Leans Democrat	1	1	52
Weak Democrat	0	0	0	52
Weak Republican	4	4	4	48
Leans Republican	2	2	44
Strong Republican	2	42
Safe Republican	40

This table summarizes the results by state. Click on the poll number to see the individual polls included for a state.

		#	Sample	Percent	Percent	Democrat	Republican
State	@	polls	size	Democrat	Republican	% wins	% wins
AL		1	1030	43.8	56.2	0.2	99.8
AK		1&	548	50.0	50.0	49.7	50.3
AZ		15	8882	54.8	45.2	100.0	0.0
AR		0	0			(0)	(100)
CO		1&	752	55.3	44.7	98.2	1.8
DE		1	712	67.8	32.2	100.0	0.0
GA		10	7259	49.6	50.4	32.6	67.4
GA		1	853	55.7	44.3	98.9	1.1
ID		1&	487	34.1	65.9	0.0	100.0
IL		1&	418	56.7	43.3	97.5	2.5
IA		5	2420	50.8	49.2	70.2	29.8
KS		2	1335	48.2	51.8	18.2	81.8
KY		2	1715	42.9	57.1	0.0	100.0
LA		0	0			(0)	(100)
ME		6	3994	53.8	46.2	99.9	0.1
MA		1&	817	55.6	44.4	98.8	1.2
MI		14	9687	52.5	47.5	100.0	0.0
MN		5	3401	55.4	44.6	100.0	0.0
MS		1&	486	49.4	50.6	41.6	58.4
MT		1	556	49.5	50.5	43.2	56.8
NE		0	0			(0)	(100)
NH		4	2797	57.4	42.6	100.0	0.0
NJ		1&	396	65.2	34.8	100.0	0.0
NM		1&	607	58.5	41.5	99.9	0.1
NC		20	14666	53.1	46.9	100.0	0.0
OK		1	380	39.5	60.5	0.1	99.9
OR		1	849	61.1	38.9	100.0	0.0
RI		0	0			(100)	(0)
SC		5	4415	49.9	50.1	46.7	53.3
SD		0	0			(0)	(100)
TN		0	0			(0)	(100)
TX		6	6033	46.4	53.6	0.0	100.0
VA		1	679	57.1	42.9	99.5	0.5
WV		0	0			(0)	(100)
WY		0	0			(0)	(100)

^@ Current party in office
^& An older poll was used (i.e. no recent polls exist).
^*Analysis assume that the two independent candidates will caucus with the Democrats.

Details of the methods are given in the FAQ.

The most recent analysis in this match-up can be found from this page.