On May 13 Wisconsin Sen. Herb Kohl (D) announced that he would not seek re-election in 2012, the eighth member — six who caucuses with Democrats, two Republicans — of the chamber to opt-out of another term.

It’s been six weeks (or so) since that day and — much to the joy of Democratic strategists — no other Senators on their side have decided to call it quits.

Stanching the flow of no-go decisions is considered essential to Democrats’ chances of holding onto their Senate majority in 2012 since open seats are traditionally more competitive than those in which an incumbent is seeking re-election.


And with Republicans needing only four seats to reclaim control — three if a GOPer is elected president — Democrats’ margins are decidedly thin.

Party strategists insisted throughout the tough few months of the cycle — when retirements in places like North Dakota, Virginia and New Mexico seemed to happen on a weekly basis — that it was part of a strategy pushed by campaign chair Patty Murray (Wash.) to push wavering members to make early decisions.

The thinking behind Murray’s approach was that a retirement early in a cycle allows the party to find the best possible replacement candidate and put the pieces in place to win. A late retirement, on the other hand — see Indiana’s Evan Bayh in the 2010 cycle — makes holding the seat far more difficult.

So far, so good.

That’s not to say that the retirements Democrats have already endured don’t make their fight to keep the Senate majority that much more difficult.

The North Dakota open seat is a goner for the party and races in Virginia, Wisconsin and New Mexico are all likely to be closely contested by the two parties. The latter two, at least, would have almost certainly remained in Democratic hands had Kohl and Sen. Jeff Bingaman decided to run in 2012.

And, we are still months — and, in many cases, more than a year — away from the first filing deadlines in states across the country. That means there is still plenty of time for Democratic Senators to reconsider their plans to run again.

But, at the moment, things are quiet on that front. And that’s good news for Democrats.

Below are the ten seats considered most likely to change party control in 2012. The number one race is the likeliest switcher. Have thoughts on our Line? Have one of your own? The comments section awaits!

To the Line!

10. Ohio (Democratic controlled): It’s been a good month for state Treasurer Josh Mande l, who is hoping to take on Sen. Sherrod Brown (D) next year. First, former Secretary of State Ken Blackwell dropped out of the race, saying he didn’t want to “make nice.” Days later, Mandel got the endorsements of Sen. Jim DeMint (R-S.C.) and the Club for Growth. Mandel still faces a challenge from former state Sen. Kevin Coughlin, but he is well on his path to the nomination. That’s where the 33-year-old Iraq veteran will face the big challenge: an incumbent who at the moment has a double-digit lead. (Previous ranking: 9)

9. Massachusetts (Republican controlled): The bad news if you’re a Democrat? You still don’t have a big name to challenge Sen. Scott Brown (R). The good news? Of the ones that are in the race, at least they’re attacking Brown, and not each other. Several of those Democratic candidates wrote a letter urging Brown to embrace gay marriage after a same-sex marriage law passed in Massachusetts. As for Elizabeth Warren’s purported interest in running for the seat, there’s really no news. The demographics of the state virtually ensure a close race no matter who Democrats nominate. (Previous ranking: 8)

8. New Mexico (D): Unlike the races listed above, both sides here have proven campaigners in and running. The question is whether either of them can make it through a primary. Both Rep. Martin Heinrich (D) and former congresswoman Heather Wilson (R) face Hispanic opponents who hold statewide office. Wilson could have trouble thanks to her moderate record, while Hispanics tend to weigh more heavily in the Democratic primary, which could complicate Heinrich’s task. If Wilson wins the nomination, this could be a surprising Republican opportunity. (Previous ranking: 10)

7. Wisconsin (D): We’re still waiting for candidates on both sides to enter this competitive open seat. Former Wisconsin Sen. Russ Feingold is still the top choice of many Wisconsin Democrats to compete for the seat being vacated by Sen. Herb Kohl (D). He’s expected to make a decision by Labor Day. Democratic Reps. Ron Kind and Tammy Baldwin might also get in sometime this summer. Former Gov. Tommy Thompson is still the likely Republican candidate, although he’s been beaten up by some national conservatives over his health-care reform record. He’s waiting until after the recall elections in the state this summer to make a final decision. (Previous ranking: 7)

6. Montana (D): The Last Best Place may well play host to the best Senate race of the 2012 cycle that no one’s heard of. The battle between Sen. Jon Tester (D) and Rep. Denny Rehberg (R) is a fascinating one. On paper, Rehberg should win given the state’s Republican lean in a presidential year. But Tester is rooted deeply in Montana — make sure to read the Post’s profile on him — and has proven to be an able politician during his first five years in office. Polling suggests this is a margin-of-error race, which is where it’s likely to stay all the way until election day. (Previous ranking: 3)

5. Virginia (D): Finally, some polling to confirm what we already knew: this will be a close race. A Quinnipiac University poll released this week showed former Democratic National Committee chairman Tim Kaine (D) at 43 percent and former senator George Allen (R) at 42 percent. When two well-known candidate run against each other in a competitive state, the race tends to stay within the margin of error. We expect nothing less here. (Previous ranking: 4)

4. Nevada (R): Democrats are increasingly optimistic in the Silver State, a confidence bolstered by a poll released by the Democratic Senatorial Campaign Committee earlier this month that put Rep. Shelley Berkley (D) ahead of Sen. Dean Heller (R) 42 percent to 37 percent. But Heller has the power of incumbency having been appointed to th e Senate following the resignation of John Ensign (R). This race will come down to how big a margin Berkley can win in Clark County (Las Vegas) and what the top-of-the-ticket dynamic will be in this swing state. (Previous ranking:6)

3. Missouri (D): Neither state Treasurer Sarah Steelman (R) nor Rep. Todd Akin (R) has distinguished themselves in the race so far. That weakness has many Republicans talking about the possibility of wealthy business John Brunner getting in the race. While the GOP field isn’t stellar, Missouri is going to be a tough state for Sen. Claire McCaskill (D) to win reelection. (Previous ranking: 5)

2. Nebraska (D): Attorney General Jon Bruning (R) leads all the other GOP hopefuls in fundraising and polls by huge margins as of last quarter. But he may have some real competition now that state Sen. Deb Fischer is in the race. The question is whether she will raise enough money to catch up. Sen. Ben Nelson (D) is clearly vulnerable in a state that is now solidly Republican, but strategists in the state caution that he should not be underestimated. (Previous ranking: 2)

1. North Dakota (D): Sen. Rick Berg (R). (Previous ranking: 1)