|A few caveats:
1. Turnout in the last two Iowa midterm elections was approximately one-third lower than in the presidential elections of 2008 and 2012. No one can say yet how many Iowans will cast ballots in the 2014 general election, but the number will be closer to 1 million than to 1.5 million. The number of votes cast in the competitive Iowa House and Senate districts will correspondingly be lower as well.
When the even-numbered Iowa Senate seats are on the ballot in 2016, the raw vote totals on this spreadsheet may be closer to the ballpark. But depending on the parties' presidential nominees, Iowa may not look like a swing state in 2016, which could mean fewer resources for GOTV on both sides.
2. Turnout doesn't drop equally among all groups of Iowa voters in midterm elections. In 2006 and 2010, turnout among independents was particularly low compared to how many no-party voters cast ballots in Iowa presidential elections. As for partisans, Iowa Democratic turnout dropped off far more in 2010 compared to 2008 than Republican turnout did.
There's no guarantee the pattern will repeat next year--for one thing, Bruce Braley's U.S. Senate campaign will have more resources for GOTV than Roxanne Conlin did in 2010 when she challenged Senator Chuck Grassley. But the Obama re-election campaign did remarkably well squeezing extra votes out of urban and suburban areas in Iowa in 2012. I wouldn't count on Iowa Democrats repeating that performance, especially since Organizing for America supposedly isn't sharing the Obama campaign's database with state Democratic parties.
3. As a general rule, Iowans like to re-elect their incumbents. Historically, lots of state representatives and senators have continued to be re-elected even when voters in their districts preferred the other party's candidate for president. So it would be a mistake to assume that every Democrat in a Romney district or every Republican in an Obama district is vulnerable in 2014.
4. If 2014 turns out to be a landslide year, a few seats that don't look competitive now may flip. Exhibit A: Mark Chelgren's surprise victory by 10 votes (!) over Democratic State Senator Keith Kreiman in Iowa's Ottumwa-based district in 2010.
Now, on to the fun stuff. The Daily Kos Elections spreadsheet includes votes in all 50 Iowa Senate districts. Democrats hold twelve and Republicans thirteen of the even-numbered seats, which won't be on the ballot until 2016. Only the 25 odd-numbered Senate districts will be on the ballot in 2014. We can quickly set aside the following uncompetitive districts.
Democratic-held Iowa Senate districts where Obama easily defeated Romney
Senate district 17 (Jack Hatch likely running for governor; Democratic candidates are Tony Bisignano, Ned Chiodo and possibly Chris Diebel)
Senate district 21 (Matt McCoy)
Senate district 23 (Herman Quirmbach)
Senate district 31 (Bill Dotzler)
Senate district 33 (Rob Hogg)
Senate district 35 (Wally Horn)
Senate district 37 (Bob Dvorsky)
Senate district 43 (Joe Bolkcom)
Senate district 45 (Joe Seng, but I wish some Democrat would challenge him in the primary)
Republican-held Iowa Senate districts where Romney easily defeated Obama
Senate district 1 (David Johnson)
Senate district 3 (Bill Anderson)
Senate district 9 (open because of Nancy Boettger's retirement, likely to be held by Jason Schultz)
Senate district 11 (Hubert Houser)
Senate district 19 (Jack Whitver)
Senate district 25 (Bill Dix)
To recap, twelve Democratic-held Iowa Senate seats won't be on the ballot in 2014, and nine more seats should be easy holds for Democrats.
Thirteen Republican-held Iowa Senate seats won't be on the ballot in 2014, and six more seats should be easy holds for the GOP.
That's a 21-19 advantage for Democrats, who currently hold a 26-24 Iowa Senate majority.
Democratic-held seats where Democrats are favored
Senate district 15 (Dennis Black)
Senate district 29 (Tod Bowman)
Senate district 49 (Rita Hart)
All of these seats should stay in Democratic hands, but I am not ready to call them uncompetitive.
In Senate district 15, Obama carried about 51.7 percent of the vote to 46.8 percent for Romney. Assuming Dennis Black runs for re-election, he should be fine. If he retires, a new Democratic candidate (possibly State Representative Dan Kelley of Newton) would be favored, given the Democratic voter registration advantage of a little more than 2,000). That said, open seats are almost always more competitive than races involving an incumbent, and we don't know yet how strong the Democratic GOTV will be next fall.
In Senate district 29, Obama carried just under 52.2 percent of the vote in 2012. I was surprised his share of the vote wasn't higher, because the district contains nearly 5,000 more Democrats than Republicans. Tod Bowman should be fine here, but because of redistricting, a lot of this territory is new to him. If Republicans recruit an unusually strong challenger, the race could become competitive.
In Senate district 49, Rita Hart is favored because Obama won more than 57 percent of the vote in 2012 and Democrats have a voter registration advantage of nearly 4,000. However, because redistricting put this empty odd-numbered seat on the ballot in 2012, first-term Senator Hart will have to face re-election after just two years instead of the usual four. Also, Republicans had a strong candidate (Andrew Naeve) in this area in 2010, and the district contains more no-party voters than Democrats.
Republican-held seats where Republicans are favored
Senate district 13 (Kent Sorenson)
Senate district 47 (Roby Smith)
Romney didn't win Senate district 13 by that much: he took about 51.4 percent of the vote to 47.2 percent for Obama. The latest voter registration numbers give Republicans an advantage of around 1,700 in the district. On the other hand, Sorenson is facing an ethics investigation and is generally an unpleasant person. Who agrees to chair one candidate's presidential campaign and jumps ship less than a week before the Iowa caucuses? Lightning could strike in this district with the right Democratic challenger, ideally someone with a strong base in Madison County.
Roby Smith represents a part of the Quad Cities that has long sent Republicans to the Iowa Senate. His district has a voter registration advantage of more than 1,700. For those reasons, I consider Smith likely to be re-elected, even though Obama defeated Romney in Senate district 47 by 50.65 percent to 48.31 percent. I don't know of any Democratic challenger here yet.
Assuming none of the districts where one party is favored change hands, Democrats would hold 24 seats and Republicans 21.
That leaves five districts that will likely determine control of the Iowa Senate in 2015 and 2016.
Democratic-held seats that will be targeted
Senate district 5 (Daryl Beall)
Senate district 27 (Amanda Ragan)
Beall and Ragan are both three-term incumbents and hard workers with a reputation for strong constituent service. Both not only survived the 2010 Republican wave, but were re-elected by comfortable margins. Redistricting made both of their districts a bit more Republican, though, and Ragan's challenger in 2010 was second-string.
Senate district 5 has only a slight Republican voter registration advantage and went to Romney by about 52.0 percent to 46.7 percent. Assuming Beall seeks a fourth term, my money is on him to win. But the Iowa GOP will target this district for sure. If Republicans find a strong candidate or Beall surprises everyone by retiring, all bets are off.
Senate district 27 has a Republican voter registration edge of about 1,400, greater than any other Democratic-held Senate district that will be on the ballot in 2014. Obama carried Ragan's district with just under 53 percent of the vote, but if Republicans recruit a challenger with strong appeal in Mason City, Ragan will face her toughest re-election battle yet. One thing she has going for her: she worked with Republican Iowa House Majority Leader Linda Upmeyer (who represents half of Senate district 27) to find the compromise alternative to expanding Medicaid in Iowa. That will be a major achievement to run on next year.
Republican-held seats that will be targeted
Senate district 7 (Rick Bertrand)
Senate district 39 (open due to Sandy Greiner's retirement)
Senate district 41 (Mark Chelgren)
First-term Senator Rick Bertrand won an open seat by only 222 votes in 2010 and now represents the GOP-held Senate district where Obama won the largest share of the vote: 56.7 percent to just 41.9 percent for Romney. That, plus a Democratic voter registration edge of more than 3,000 put Bertrand high on the target list. However, this race will not be a gimme for Iowa Democrats. The Obama campaign had tremendous GOTV in Woodbury County in 2012, which may or may not be repeated next year. Bertrand is a local bar owner and a lot more personable than Romney. I am not aware of any declared challenger in Senate district 7. Democrats need to find someone with a lot of stature in Sioux City, as Democratic turnout is generally low here compared to other Iowa cities.
Senate district 39 looks like a classic tossup race, with no incumbent and no voter registration advantage for either party. Republicans have one announced candidate. I haven't heard of any Democrat running here yet. Half the district lies in Johnson County, putting it within easy striking distance for volunteers in the Iowa City area.
Senate district 41 is probably the GOP's most at-risk seat. Democrats were blindsided by Mark Chelgren's squeaker in 2010 in a district neither party's strategists had their eyes on. (The incumbent was door-knocking for Becky Schmitz in a neighboring district the weekend before election day.) Democrats are highly motivated to take back this district containing Ottumwa and Fairfield, where Democrats currently outnumber Republicans by more than 3,500. Obama carried just under 53 percent of the vote in Senate district 41. To my knowledge, no Democrat has announced a challenge to Chelgren, but at least one person in Wapello County is strongly considering the race.
Democrats need to win at least two of the five most competitive districts to retain control of the Iowa Senate.