In the bat­tle for the Sen­ate, most states remain unchanged from last time, but there was one notable excep­tion. And our cat­e­go­riza­tion cri­te­ria will be chang­ing soon, as I’ll explain in my summary.

Here is the cur­rent map:

Now for the details.

As always, “Con­tin­u­ing” refers to the seats in Sen­ate Classes 2 and 3, which are not up for elec­tion this cycle.

With Nate Silver’s new cal­cu­la­tions of poll­ster house effect biases, I’m able to bet­ter assess the prospects of the var­i­ous candidates.

Here the high­lights of the past two weeks, walk­ing from the Pacific to the Atlantic:

  • Wash­ing­ton: I men­tion the Ever­green State only to observe that incum­bent Demo­c­ra­tic Sen­a­tor Maria Cantwell is still polling far ahead of her most likely oppo­nent, state Sen­a­tor Michael Baum­gart­ner. While the poll was con­ducted by Pub­lic Pol­icy Polling, the 16-​​point mar­gin, which con­verts to an 11-​​point adjusted likely voter mar­gin, is suf­fi­ciently great as to main­tain Wash­ing­ton state deep in the “Lean Demo­c­ra­tic” column.
  • Nevada: Real Clear Pol­i­tics con­tin­ues to call Nevada a tossup. The recent poll from Pub­lic Pol­icy Polling has incum­bent Repub­li­can Sen­a­tor Dean Heller with a one-​​point lead over his likely oppo­nent, Rep­re­sen­ta­tive Shel­ley Berkley (D-​​Las Vegas). This trans­lates to an adjusted five-​​point Heller lead. I remain in oppo­si­tion to RCP on their take; it’s a “Leans Repub­li­can” state.
  • Ari­zona: The only new infor­ma­tion we have here is a sin­gle poll from Project New America/​Public Pol­icy Polling, show­ing Rep­re­sen­ta­tive Jeff Flake (R-​​Mesa) with a two-​​point mar­gin over the only declared Demo­c­rat in the race, for­mer United States Sur­geon Gen­eral Richard Car­mona. Unlike past polls from PPP, this one uses a “likely voter” model, which should shade the results about 1.6 points to the right of their usual posi­tion­ing. This puts Flake about five points ahead of Car­mona. Real Clear Pol­i­tics con­sid­ers Ari­zona a “Leans Repub­li­can” state, and I agree.
  • Mon­tana: Ras­mussen has a new poll, indi­cat­ing a two-​​point lead for Rep­re­sen­ta­tive Denny Rehberg (R) over incum­bent Demo­c­ra­tic Sen­a­tor Jon Tester. The lat­est poll makes Rasmussen’s May poll look like an out­lier, and sug­gests that less than a point sep­a­rates the two can­di­dates. I now believe I was too quick to move Mon­tana to “Lean Repub­li­can”, and so I’m mov­ing it back into the Land of the Purple.
  • North Dakota: I’m still wait­ing for more data before mov­ing North Dakota from “Lean Repub­li­can” to “Tossup”, but my gut says it prob­a­bly should be moved.
  • Nebraska: There’s one new poll from Ras­mussen, con­firm­ing what we already know. Repub­li­can state Sen­a­tor Deb Fis­cher has a com­mand­ing lead over her Demo­c­ra­tic rival, for­mer Sen­a­tor Bob Ker­rey. This is the sin­gle most likely flip of the election.
  • Wis­con­sin: Res­i­dents of the Bad­ger State are get­ting bad­gered by poll­sters. For­mer Gov­er­nor Tommy Thomp­son remains the most likely Repub­li­can to face off against Rep­re­sen­ta­tive Tammy Bald­win (D-​​Madison), and Thomp­son has a pretty solid lead: by eight points, accord­ing to Mar­quette Uni­ver­sity, and 16 points, accord­ing to Ras­mussen. The two don’t align in mar­gin, even account­ing for house effects, but all polls point to Thomp­son. Real Clear Pol­i­tics calls Wis­con­sin a tossup; I call it “Lean Republican”.
  • Michi­gan: Since we last looked, Ras­mussen and EPIC-​​MRA have both released polls on this Sen­ate race. Both indi­cate that incum­bent Sen­a­tor Deb­bie Stabenow has a com­mand­ing lead over the per­sump­tive Repub­li­can nom­i­nee, for­mer Rep­re­sen­ta­tive Pete Hoek­stra (R-​​Zeeland). So many signs have been point­ing to about a ten-​​point Stabenow likely-​​voter lead for so long that, bar­ring a trend to the right show­ing up in the next two weeks, I’m going to move Michi­gan to “Likely to Stay Demo­c­rat” in our next installment.
  • Vir­ginia: With the house effect data more clearly defined, Vir­ginia seems pretty con­sis­tently a point or two in for­mer Gov­er­nor Tim Kaine’s favor, over for­mer Gov­er­nor George Allen. This puts Vir­ginia on the cusp of being called “Lean Demo­c­ra­tic”, pro­vided the con­sis­tency per­sists until August.
  • Florida: Now that for­mer Sen­a­tor George LeMieux has dropped out of the race, it’s all but cer­tain that the Repub­li­can nom­i­nee will be Rep­re­sen­ta­tive Con­nie Mack, IV (R-​​Fort Mey­ers). Quinnipiac’s poll from last time, which showed a lead for Mack over Demo­c­ra­tic incum­bent Sen­a­tor Bill Nel­son, now looks like an out­lier. Their new poll, with a four-​​point Nel­son lead, is more con­sis­tent with the broader trend. There appears to be more fluc­tu­a­tion in Florida’s Sen­ate can­di­date polling results, even account­ing for house effects, so it’s likely that the sit­u­a­tion is less sta­ble here than in, say, Nevada or Michi­gan, or even Vir­ginia. The Sun­shine State con­tin­ues to look like it’s just barely into “Leans Demo­c­ra­tic” ter­ri­tory. Real Clear Pol­i­tics calls Florida a tossup, and I could be con­vinced to do the same, based on activ­i­ties the state gov­ern­ment is doing to depress Demo­c­ra­tic turnout.

Start­ing in July, the zones will nar­row, so it will take fewer points in spread to leave the “Tossup” col­umn for one of the “Leans” columns, and also fewer points to go from “Leans” to “Likely”. This results from a com­bi­na­tion of hav­ing more data points, which reduces error, and less remain­ing time for any can­di­date to move the needle.

As it has been for some time, the major­ity of the 113th Sen­ate hangs in the bal­ance. There are four tossups: Indi­ana, Mass­a­chu­setts, Mon­tana, and Vir­ginia; plus a fifth that prob­a­bly belongs there: North Dakota. It seems cred­i­ble for Repub­li­cans to win at least three of those five, since they have struc­tural advan­tages in all five. This is prob­a­bly why Intrade is giv­ing Repub­li­cans about a 57 per­cent chance of tak­ing the Sen­ate, up two points from two weeks ago, with a 32 per­cent chance of Democ­rats hold­ing at least 51 seats (up six points from last time), and 17 per­cent chance of exactly 50 seats (up three points). Note that the three add up to 106 per­cent, which I believe reflects more about how lightly traded these mar­kets are than any­thing else.

How cred­i­ble do you think those mar­ket num­bers are? Do you agree or dis­agree with my state analy­ses above?

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