Who Wins the Senate?

The presidential race isn’t the only thing happening tomorrow. We’re also electing 33 senators and the entire House of Representatives. Conventional wisdom says that the Democrats might gain a few seats in the House, but not enough to win a majority. I don’t have anything to add to that; 435 races are too many for me to get a handle on.

The Senate is another story. There are only 100 senators, and we only elect 1/3 of them at a time. This year 67 senators are not up for election — 30 Democrats and 37 Republicans.

Sure wins. Some of those 33 races aren’t very competitive. Nate Silver’s polling aggregation model gives a better than 95% chance of victory to 13 Democrats (Hirono in Hawaii, Cantwell in Washington, Feinstein in California, Klobuchar in Minnesota, Stabenow in Michigan, Brown in Ohio, Casey in Pennsylvania, Gillibrand in New York, Whitehouse in Rhode Island, Menendez in New Jersey, Cardin in Maryland, Carper in Delaware, and Nelson in Florida), 6 Republicans (Hatch in Utah, Barrasso in Wyoming, Fischer in Nebraska, Cruz in Texas, Wicker in Mississippi, and Corker in Tennessee), and 1 independent (Sanders in Vermont).

Sanders caucuses with the Democrats, so if all those races turn out as expected we’re up to 44 Democrats and 43 Republicans.

Now let’s do the same thing we did in the electoral college analysis and put the remaining 13 races in order, starting with the one that has the greatest likelihood of a Democratic win, and ending with the least likely Democratic win.

93.6% Warren/Brown in Massachusetts

93.0% Heinrich/Wilson in New Mexico

92.2% King/Dill/Summers (King is an independent expect to caucus with the Democrats)

92.2% Murphy/McMahon in Connecticut

89.7% Manchin/Raese in West Virginia

88.3% McCaskill/Akin in Missouri

85.0% Kaine/Allen in Virginia

77.2% Baldwin/Thompson in Wisconsin

67.7% Donnelly/Mourdock in Indiana

31% Tester/Rehberg in Montana

23.% Berkley/Heller in Nevada

19.6% Cremona/Flake in Arizona

10.5% Heitkamp/Berg in North Dakota

If you assume all the favorites win, that gives the Democrat a 53-47 advantage, the same as they have now. If President Obama is re-elected, the Democrats will need only 50 votes to control the Senate (because the vice president casts the tie-breaking vote). So they will hold the majority even if they only win the top six races on this list.

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