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.



Image courtesy of The Upshot

Nate Silver's FiveThirtyEight model now has Republican chances of winning the Senate at 55 percent, down from 64 percent 12 days ago. "The two states with the largest shifts have been Colorado and North Carolina — in both cases, the movement has been in Democrats’ direction," Silver writes. "That accounts for most of the difference in the forecast."

It's important to note that these models change daily as new polling is released and factored in. So, tomorrow it's possible that Election Lab will show Republicans with a very narrow edge in the battle for the Senate. What you should take away from the models then is a) all three have moved toward Democrats of late and b) all three show the battle for the Senate majority to be the truest of tossups at the moment.

What's interesting about the election models is that they are moving in the opposite direction of political handicappers. In recent days, Stu Rothenberg and Charlie Cook, the two best-known, nonpartisan prognosticators in Washington, have each written that the possibility of large-scale Republicans gains is increasing, not decreasing. Wrote Stu last week:

After looking at recent national, state and congressional survey data and comparing this election cycle to previous ones, I am currently expecting a sizable Republican Senate wave. The combination of an unpopular president and a midterm election (indeed, a second midterm) can produce disastrous results for the president’s party. President Barack Obama’s numbers could rally, of course, and that would change my expectations in the blink of an eye. But as long as his approval sits in the 40-percent range (the August NBC News/Wall Street Journal poll), the signs are ominous for Democrats.

These two sets of predictions are not mutually exclusive. Charlie and Stu are trying to look ahead seven weeks to predict the outcome; the election models are measuring the chances as of today. Still, it's a fascinating split — and one to watch over the final seven weeks of the 2014 election.