The battle for control of the Senate is a pure toss-up. Not just like a this-is-very-close toss-up, but like a 50-50-odds toss-up. Our team ran 10,000 simulations using our most recent ratings of the 36 seats up for grabs on Nov. 4. It showed Republicans with a 50.03 percent chance of winning the Senate and Democrats with a 49.97 percent chance of holding the Senate. Again: pure toss-up.
Ben Highton asks, “What explains this over-performance by Democrats, or under-performance by Republicans?”
One possibility is that the “midterm penalty” — the loss in vote share suffered by the president’s party in the midterm — is shaping up to be smaller than in the past. That penalty is estimated by comparing midterm and presidential election years from 1980-2012. For 2014, we have applied the average penalty, taking into account uncertainty due to variation in past midterm penalties along with the uncertainty that arises simply because 2014 is a new election year. But it is plausible that the size of the midterm penalty in 2014 may end up being smaller than in the past. This could be the consequence of voter discontent with the Republican Party, as Nate Cohn has noted.
Another possibility is that there are idiosyncratic features of individual races that the background fundamentals cannot easily capture, and which favor Democrats in certain races. For example, maybe some candidates in the key races are just better or worse in ways that we cannot easily measure — but that the polls are capturing.
Harry Enten presumes that the Democrats’ advertising advantage has played a role:
Democratic Senate candidates and the outside groups supporting them have enjoyed advertising edges in almost all the competitive Senate contests over the past few weeks. Three of their larger advertising leads have been in Colorado, Michigan and North Carolina — the three states where we’ve seen the biggest movements toward Democratic candidates in the FiveThirtyEight forecasts. New Hampshire, one of the few competitive states to move toward the GOP over the last week, is also one of the few states where Republicans have had an advertising advantage. …
The question is whether Republicans and their affiliated groups can catch up. If they can, then we may see a reversion to the mean, and the Republicans’ more robust position might be restored. If Democrats maintain their lead on the air — and if that edge is what’s driving the Democratic run over the past few days — then they might able to overcome a bad national environment.
Andrew Prokop provides more details on the Democrats’ advertising edge:
Some of this advantage is because more Democratic incumbents are at risk, and incumbents usually have an easier time raising money than challengers. But Democrats are getting substantial support from Super PACs and dark money groups as well — the Washington Post’s Matea Gold describes how close allies of Senate Majority Leader Harry Reid are coordinating a major outside spending effort. The top disclosed donors to these pro-Democratic groups include wealthy financiers Tom Steyer and James Simons, as well as media mogul Fred Eychaner and former New York City Mayor Michael Bloomberg, and several unions, according to BOpenSecrets.
Recent Dish on the Senate races here.