Which U.S. Senate Seats Have Had the Most Partisan Turnover?

Six seats up for election in 2012 rank in the top 10 for the most frequent change in party control since the introduction of popular vote elections, including Sherrod Brown’s (OH), Claire McCaskill’s (MO), and Joe Lieberman’s (CT)

With Republicans falling just a few seats shy of taking control of the U.S. Senate last November, the media is already honing in on those seats currently held by Democrats that might flip in two years.

D.C. prognosticators are helping to lead the charge – not allowing any dust to settle on their slide rules or abacuses – with several already handicapping a 2012 election cycle that finds Democrats needing to defend 23 of 33 seats.

Among the seats considered most likely to switch parties are those held by Democrats Ben Nelson (NE), Jim Webb (VA), Joe Manchin (WV), Sherrod Brown (OH), Claire McCaskill (MO), Bill Nelson (FL), and (independent-Democrat) Joe Lieberman (CT), and Republicans Scott Brown (MA) and John Ensign (NV).

But how frequently do Senate seats actually flip parties?

A Smart Politics review of the more than 1,500 U.S. Senate contests conducted since popular vote elections were introduced 100 years ago finds the average partisan hold on a Senate seat is 36 years.

The average Senate seat has changed partisan control just 4.2 times since its first popular vote election (which ranges from 1906 with Oregon’s Class II seat, to 1918 for the 25 remaining Class II seats, to the four seats from Alaska and Hawaii in the late 1950s).

However, among those seats considered most likely to switch parties in 2012 are those that historically have been the most politically schizophrenic in the nation.

Overall, six of the Top 10 seats with the highest frequency of partisan turnover are on the ballot in two years: the Class I Senate seats from Ohio (Sherrod Brown), Missouri (Claire McCaskill), Connecticut (Joe Lieberman), Michigan (Debbie Stabenow), New Jersey (Robert Menendez), and Maryland (Ben Cardin).

But the two seats with the greatest partisan turnover across the last 100 years will not be on the ballot in 2012.

At the top of the list is Colorado’s Class III seat – narrowly held by Democrat Michael Bennet in 2010 by less than two points against GOP challenger and Tea Party favorite Ken Buck.

Bennet’s seat has flipped 12 times since its first popular vote election in 1914, for an average of once every 8.1 years – or 4.4 times shorter than the national average of 36 years.

Democrat Charles Thomas was the first popularly elected U.S. Senator to the seat – holding it for a term until losing his reelection bid to Republican Samuel Nicholson in 1920. Nicholson would die in office after just two years, and a Democrat, Alva Adams, was appointed to the seat. Adams, however, retired after just one and a half years, and Republicans took back the seat in December 1924 with the election of Rice Means.

Partisan control of Colorado’s Class III seat would then go on to change another nine times over the next eight decades: in 1932 (to the Democrats), 1932 again (to the GOP), 1933 (Democrat), 1941 (GOP), 1957 (Democrat), 1963 (GOP), 1975 (Democrat), 1995 (GOP, when Ben Nighthorse Campbell switched parties), and 2005 (Democrat, with the election of Ken Salazar).

Just behind is Minnesota’s Class II seat, currently held by top GOP target Al Franken.

Minnesota’s Class II seat has also seen shifts in political control 12 times over the past century – including four times over the last two decades: in 1991 (DFLer Paul Wellstone), 2002 (Independence Party appointee Dean Barkley), 2003 (GOPer Norm Coleman) and 2009 (DFLer Franken).

This seat was first on the ballot in 1912, and has thus seen a change in control every 8.3 years.

But 2012 also finds several historically turbulent seats on the ballot, beginning with Sherrod Brown’s Class I seat, which the GOP has marked with one of its biggest bulls-eyes .

Brown’s seat has flipped 10 times since its first popular vote election in 1916, or once every 9.5 years – the third most in U.S. history.

Half of these changes in partisan control have occurred with incumbents losing reelection: Democrat Atlee Pomerene (in 1922) and Republicans Simeon Fess (1934), John Bricker (1958), Robert Taft (1976), and Mike DeWine (2006).

Claire McCaskill’s Senate seat in Missouri has been another topsy-turvy seat, notching the 8th most frequent turnover in party control in history.

The seat has endured eight such changes since its first popular vote election in 1916, or once every 11.9 years.

Former Missouri State Treasurer Sarah Steelman quickly jumped into the race to challenge McCaskill, just a few weeks after the 2010 GOP landslide.

Other Class I seats up for election in 2012 that have produced a much higher than normal change in partisan control include:

· New Jersey at #7 (held by Robert Menendez): nine instances, or once every 10.6 years
· Maryland at #9 (Ben Cardin): eight instances, or once every 12.3 years
· Connecticut at #10 (Joe Lieberman): seven instances, or once every 13.6 years
· Michigan at #10 (Debbie Stabenow): seven instances, or once every 13.6 years

But while these seats have provided many dramatic shifts in the partisan preferences of the electorate, many have not.

In fact, more than half of U.S. Senate seats have flipped four times or fewer during the past 100 years (52 seats).

Three seats have never changed partisan control since the introduction of popular vote elections a century ago – all held by Democrats:

· Montana’s Class II seat (first popular elections in 1912): held by Democrats Thomas Walsh, John Erickson, James Murray, Lee Metcalf, Paul Hatfield, and Max Baucus

· Louisiana’s Class II seat (1918): held by Democrats Joseph Ransdell, Huey Long, Rose Long, Allen Ellender, Elaine Edwards, J. Bennett Johnston, and Mary Landrieu.

· Hawaii’s Class III seat (1959): held by Democrats Oren Long and Daniel Inouye.

Another 17 U.S. Senate seats have seen a change in partisan control just one time: the Class I seats in Hawaii, Mississippi, North Dakota, Texas, and Vermont, the Class II seats in Alabama, Georgia, Kansas Mississippi, Rhode Island, South Carolina, and Texas, and the Class III seats in Alaska, Arkansas, Louisiana, South Carolina, and Vermont.

Frequency of Change in Partisan Control of U.S. Senate Seats Since Popular Vote Elections

Rank	State	Class	#	1st Election	Years per flip
1	Colorado	3	12	1914	8.1
2	Minnesota	2	12	1912	8.3
3	Ohio	1	10	1916	9.5
4	Ohio	3	10	1914	9.7
5	Iowa	2	9	1918	10.3
5	Kentucky	2	9	1918	10.3
7	New Jersey	1	9	1916	10.6
8	Missouri	1	8	1916	11.9
9	Maryland	1	8	1913	12.3
10	Connecticut	1	7	1916	13.6
10	Michigan	1	7	1916	13.6
12	Indiana	3	7	1914	13.9
12	South Dakota	3	7	1914	13.9
12	Wisconsin	3	7	1914	13.9
15	Oklahoma	2	7	1912	14.1
16	Oregon	3	7	1908	14.7
17	Wyoming	2	6	1918	15.5
18	Delaware	1	6	1916	15.8
18	Indiana	1	6	1916	15.8
18	Nebraska	1	6	1916	15.8
18	New Mexico	1	6	1916	15.8
18	New York	1	6	1916	15.8
23	Idaho	3	6	1914	16.2
23	Illinois	3	6	1914	16.2
23	Maryland	3	6	1914	16.2
23	Pennsylvania	3	6	1914	16.2
27	Colorado	2	6	1912	16.5
28	Nevada	1	6	1910	16.8
29	Nevada	3	6	1908	17.2
30	Delaware	2	5	1918	18.6
30	Illinois	2	5	1918	18.6
30	Michigan	2	5	1918	18.6
30	South Dakota	2	5	1918	18.6
30	West Virginia	2	5	1918	18.6
35	California	1	5	1916	19.0
35	Minnesota	1	5	1916	19.0
35	Pennsylvania	1	5	1916	19.0
35	Virginia	1	5	1916	19.0
35	Washington	1	5	1916	19.0
35	West Virginia	1	5	1916	19.0
41	Connecticut	3	5	1914	19.4
41	Florida	3	5	1914	19.4
41	Georgia	3	5	1914	19.4
41	Kentucky	3	5	1914	19.4
41	Missouri	3	5	1914	19.4
41	New York	3	5	1914	19.4
41	North Carolina	3	5	1914	19.4
48	Oregon	2	5	1906	21.0
49	Idaho	2	4	1918	23.3
49	Massachusetts	2	4	1918	23.3
49	Nebraska	2	4	1918	23.3
52	Massachusetts	1	4	1916	23.8
52	Montana	1	4	1916	23.8
52	Rhode Island	1	4	1916	23.8
55	California	3	4	1914	24.3
55	Iowa	3	4	1914	24.3
55	New Hampshire	3	4	1914	24.3
55	North Dakota	3	4	1914	24.3
59	Alaska	2	2	1958	26.5
60	New Hampshire	2	3	1918	31.0
60	New Jersey	2	3	1918	31.0
60	New Mexico	2	3	1918	31.0
60	Tennessee	2	3	1918	31.0
64	Tennessee	1	3	1916	31.7
64	Utah	1	3	1916	31.7
64	Wisconsin	1	3	1916	31.7
64	Wyoming	1	3	1916	31.7
68	Alabama	3	3	1914	32.3
68	Oklahoma	3	3	1914	32.3
68	Washington	3	3	1914	32.3
71	Arizona	1	3	1912	33.0
71	Arizona	3	3	1912	33.0
73	Arkansas	2	2	1918	46.5
73	Maine	2	2	1918	46.5
73	North Carolina	2	2	1918	46.5
73	Virginia	2	2	1918	46.5
77	Florida	1	2	1916	47.5
77	Maine	1	2	1916	47.5
79	Kansas	3	2	1914	48.5
79	Utah	3	2	1914	48.5
81	Hawaii	1	1	1959	52.0
82	Alaska	3	1	1958	53.0
83	Alabama	2	1	1918	93.0
83	Mississippi	2	1	1918	93.0
83	Rhode Island	2	1	1918	93.0
83	South Carolina	2	1	1918	93.0
83	Texas	2	1	1918	93.0
88	Mississippi	1	1	1916	95.0
88	North Dakota	1	1	1916	95.0
88	Texas	1	1	1916	95.0
88	Vermont	1	1	1916	95.0
92	Arkansas	3	1	1914	97.0
92	Georgia	2	1	1914	97.0
92	Louisiana	3	1	1914	97.0
92	South Carolina	3	1	1914	97.0
92	Vermont	3	1	1914	97.0
97	Kansas	2	1	1912	99.0
98	Hawaii	3	0	1959	None
98	Louisiana	2	0	1918	None
98	Montana	2	0	1912	None

Data compiled by Smart Politics.

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