The Primary Questions

Democrats, bolstered by Republican Sen. Olympia Snowe's surprise retirement in Maine, still feel good about their chances of keeping control of the upper chamber. There are enough Republican seats in play, and strong enough Democratic incumbents, that the party believes the GOP would have to virtually run the table to put Minority Leader Mitch McConnell back in charge.

But those assumptions may be premature, as this month showed: A series of public polls in Massachusetts cast Sen. Scott Brown's reelection hopes in a better light. Ethics questions surrounding Rep. Shelley Berkley, D-Nev., have Republicans optimistic they can survive President Obama's turnout operations. And even as Sens. Bill Nelson and Sherrod Brown flex their healthy polling leads, Sens. Claire McCaskill and Jon Tester are still shaky as ever. Finally, Republicans who are pessimistic about the presidential race increasingly view the battle for the Senate as the biggest game in town, raising the prospects that super PACs that give up on the eventual GOP nominee could pour unanswered millions into those down-ballot contests.

The final retirements of the year have taken place, and primary season is in full swing. The outcomes in several states will determine which party actually holds the power when the 113th Congress convenes.

In this, the fifth installment of Hotline's monthly Senate rankings, we examine the seats most likely to change partisan control in next year's elections. That is, we see Sen. Ben Nelson's seat in Nebraska as more likely to wind up in Republican hands than Sen. Kent Conrad's seat in North Dakota (but not by much), and Scott Brown more likely to lose to a Democrat than Sen. Dean Heller of Nevada. Our complex methodology includes a delicate balance of poll numbers, both public and private; fundraising performance; message resonance; buzz on the trail; and, the key ingredient, our gut feelings. From those five factors, we answer a fundamental question: Which candidate would we rather be? In North Dakota, we'd rather be Rep. Rick Berg than former Attorney General Heidi Heitkamp, for example.

The ultimate conclusions are subjective, of course. But they represent months of close scrutiny of each race and our best conclusions as to where the Senate is headed in the 113th Congress.

1.
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NEBRASKA (Open D, Sen. Ben Nelson retiring) (Last month's rank: 1)
The cloud hanging over the most vulnerable Democratic open seat got a ray of sunshine when former Sen. Bob Kerrey decided to run. But even those clouds can produce rain. Kerrey's rollout hasn't been smooth, while polling suggests the GOP's favored candidate--Attorney General Jon Bruning--is well ahead in both the primary and the general.

2.
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NORTH DAKOTA (Open D, Sen. Kent Conrad is retiring) (Last month: 2)
Rep. Rick Berg has been quietly dumping a serious amount of money into early television ads. He has a primary he has to get through, but the ads lay groundwork for a general election. Former state Attorney General Heidi Heitkamp is putting distance between herself and the Obama administration on the Keystone XL pipeline, but that may not work in a red state in a presidential year.

3.
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MAINE (Open R, Sen. Olympia Snowe retiring) (Last month: 4)
The absence of any top-tier--or even B-level--Democratic candidate in the race is by design: Democrats are rallying around former Gov. Angus King, even though some lower-tier candidates aren't happy about that. Republicans will face a primary, and if they can't prop up a Democrat enough to take votes away from King, Snowe's seat is gone.

4.
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MISSOURI (D, Sen. Claire McCaskill) (Last month: 3)
McCaskill has her vulnerabilities, and Republicans think she's in as bad a political position as Sen. Blanche Lincoln was in 2010. Expect Republicans to delve into McCaskill's votes, with the stimulus playing a bigger role here than in other states. But the GOP field is so weak and splintered that it gives her hope of keeping her job. (See our baseline analysis of the race here.)

5.
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MONTANA (D, Sen. Jon Tester) (Last month: 6)
Both Tester and Rep. Denny Rehberg are running away from their parties to some extent. Rehberg has voted repeatedly against Rep. Paul Ryan's budget, making it difficult for Democrats to box him in, while Tester's populism gives him crossover appeal. But Tester's ceiling is lower in a presidential year than it was in 2006, and some independent observers wonder if he can break 50 percent.

6.
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MASSACHUSETTS (R, Sen. Scott Brown) (Last month: 5)
Public polls lately have shown Brown ahead in the high single-digits. In reality, polling conducted for both parties still shows that the race is a dead heat. The anti-super PAC pledge both Brown and Democrat Elizabeth Warren signed looks like a bad decision for Warren, but it also eliminates activism by groups that prove most effective at raising a candidate's negatives. If Warren has higher approval ratings than Brown in November, she will win.

7.
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WISCONSIN (Open D, Sen. Herb Kohl retiring) (Last month: 8)
Republicans need to avoid a bloody primary that appeals to the base more than Wisconsin's still-left leaning electorate. If the eventual GOP nominee looks relatively healthy after the Aug. 14 primary, he will have a good shot to beat Rep. Tammy Baldwin. But Baldwin has laid low and is stockpiling cash and building a good structural foundation. How the Democrat positions herself for moderate voters may determine her fate.

8.
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NEVADA (R, Sen. Dean Heller) (Last month: 7)
Both Republican Heller and Democrat Shelley Berkley need to run a near-perfect race to win this year. A front-page New York Times story questioning Berkley's ethics last fall was a minor inconvenience; a continuing ethics investigation just gives Heller's team more ammunition. Berkley needs a strong Obama ground game more than perhaps any Democratic candidate; given Nevada's status as a swing state, she'll benefit. But her margin for error is shrinking. (See our baseline analysis of the race here.)

9.
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VIRGINIA (Open D, Sen. Jim Webb retiring) (Last month: 9)
Even with Republican Gov. Bob McDonnell's positive approval rating, Democrats haven't lost a statewide race in an even year in Virginia since 2004. That speaks to the state's changing demographics--and to Democrat Tim Kaine's inherent advantage. Republican George Allen's campaign will need to tie Kaine to Obama better than they have, and hope the president becomes an albatross. (See our baseline analysis of the race here.)

10.
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NEW MEXICO (Open D, Sen. Jeff Bingaman retiring) (Last month: 10)
Former Republican Rep. Heather Wilson has a much clearer primary field, something conservatives who targeted her early didn't expect. She'll have to overcome her party's tarnished image among Hispanics, but Wilson is the ideal candidate to do that. Rep. Martin Heinrich is the DSCC's favored candidate, but he'll have to beat a Hispanic rival in a Democratic primary that includes a big number of Hispanic voters.

11.
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FLORIDA (D, Sen. Bill Nelson) (Last month: 11)
Rep. Connie Mack is the front-runner in the race to take on Nelson, but stories about his adventures as a younger man aren't helping his case. A month ago, this race looked like it could get close. It still can, but the most recent public polling suggests that Nelson leads by a statistically significant margin.

12.
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OHIO (D, Sen. Sherrod Brown) (Last month: 13)
Brown, like Bill Nelson, is only likely to lose if he gets swept up in an anti-Democratic wave. His approval ratings are still solid, and he's up by 10 points in a Quinnipiac poll out this week. Josh Mandel has the potential to become a very good candidate, but his rollout and questions over his commitment to his current job leave much room for improvement.

13.
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MICHIGAN (D, Sen. Debbie Stabenow) (Last month: 15)
Stabenow's approval ratings have never been good. Even in 2006, as she cruised toward reelection, voters didn't think she deserved another term. But Michigan is starting to resemble New Jersey--a state that always tantalizes Republicans but never delivers at the federal level. Stabenow needs to hang on to the voters most effected by the auto bailouts; if she doesn't, former Rep. Pete Hoekstra could present a surprisingly difficult challenge.

16.
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HAWAII (Open D, Sen. Daniel Akaka retiring) (Last month: 12)
Former Gov. Linda Lingle is doing about as well as a Hawaii Republican can do, and the chamber of commerce is helping out with early advertisements. But in an era in which voters are less likely to split tickets, Lingle's chances are complicated by Obama's presence at the top of the ticket. Both national Democrats and Republicans want Rep. Mazie Hirono to be the Democratic nominee, albeit for very different reasons.

14.
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ARIZONA (Open R, Sen. Jon Kyl retiring) (Last month: 17)
Democrats are trying something clever: They hope former Surgeon General Richard Carmona can boost Hispanic turnout enough to drive the state into the competitive column at the presidential level. But Rep. Jeff Flake's position on immigration is closer to John McCain's than it is to Jan Brewer's, and even in 2008 McCain took 40 percent of the nonwhite vote against Obama. Arizona will be a swing state; this year may just be a cycle too soon. (See our baseline analysis of the race here.)

15.
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INDIANA (R, Sen. Richard Lugar) (Last month: 14)
Lugar's odds in the primary get worse every day he's forced to acknowledge he doesn't even live in the state. Democrats believe that their opposition research file on state Treasurer Richard Mourdock is hefty enough to make this a race, but Rep. Joe Donnelly isn't raising the money it would take to put him in a position to capitalize. Outside groups aren't going to be interested in Donnelly if his campaign keeps resembling a quixotic tilting at windmills.

17.
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CONNECTICUT (Open ID, Sen. Joe Lieberman retiring) (Last month: 16)
Former Rep. Christopher Shays runs better against any Democrat than wrestling executive Linda McMahon, but McMahon's money is making her the favorite in the primary. If Rep. Chris Murphy can emerge from his own primary relatively unscathed, the state's political landscape favors his campaign this year--even if McMahon does spend another $50 million.

18.
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PENNSYLVANIA (D, Sen. Robert Casey) (Last month: 18)
In the right year, under the right circumstances, with the right opponent, Casey could be vulnerable. Republicans don't have the right candidate, Obama is doing well in the state, and the economy is getting better. Strike one, strike two, strike three.

19.
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WEST VIRGINIA (D, Sen. Joe Manchin) (Last month: 20)
The rest of the South has moved toward the Republicans, and some day West Virginia will too. But Manchin has positioned himself further away from Obama than any other Democrat in the Congress--he brags about never visiting the White House--and his opponent is a subpar rerun. This won't be the year Republicans win back the Mountineer State.

20.
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NEW JERSEY (D, Sen. Robert Menendez) (Last month: 19)
Polls still show New Jersey voters don't like Menendez, but that doesn't mean state Sen. Joe Kyrillos has a good chance. He raised big bucks at an early fundraiser with Republican Gov. Chris Christie, but he's unlikely to get much attention from national sources unless Menendez really screws up or the landscape shifts dramatically. If we're talking about New Jersey in October, we're talking about a near-supermajority Senate.