Democrats now have a 51 percent chance of holding the Senate

Democrats are now (very slightly) favored to hold the Senate majority on Nov. 4, according to Election Lab, The Post’s statistical model of the 2014 midterm elections.

Election Lab puts Democrats’ chances of retaining their majority at 51 percent — a huge change from even a few months ago, when the model predicted that Republicans had a better than 80 percent chance of winning the six seats they need to take control. (Worth noting: When the model showed Republicans as overwhelming favorites, our model builders — led by George Washington University’s John Sides — warned that the model could and would change as more actual polling — as opposed to historical projections — played a larger and larger role in the calculations. And, in Republicans’ defense, no one I talked to ever thought they had an 80 percent chance of winning the majority.)

So, what exactly has changed to move the Election Lab projection? Three big things:

* Colorado: On Aug. 27 — the last time I wrote a big piece on the model — Election Lab said Sen. Mark Udall (D) had a 64 percent chance of winning. Today he has a 94 percent chance.

* Iowa: Two weeks ago, the model gave state Sen. Joni Ernst (R) a 72 percent chance of winning. Today she has a 59 percent chance.

* Kansas: Republican Sen. Pat Roberts’s reelection race wasn’t even on the radar on Aug. 27. Today, Election Lab predicts that he has just a 68 percent chance of winning.

In addition to that trio of moves in Democrats’ direction, Louisiana has moved slightly in Democrats’ favor (from a 57 percent chance of losing to a 53 percent chance), as has North Carolina (a 97 percent chance of winning now as opposed to a 92 percent chance on Aug. 27).

By contrast, Alaska has moved in Republicans’ direction (Democratic Sen. Mark Begich’s chances of winning are down from 66 percent to 53 percent), and Georgia has become more of a sure-thing hold (a 91 percent GOP win vs. an 84 percent hold).

The movement toward Democrats in the Election Lab model isn’t unique. LEO, the New York Times’ Upshot model, gives Republicans a 51 percent chance of winning the Senate — but that is down significantly over the past few weeks.

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