Nate Silver updated his Senate forecast yesterday:
It’s still early, and we should not rule out the possibility that one party could win most or all of the competitive races.
It can be tempting, if you cover politics for a living, to check your calendar, see that it’s already August, and conclude that if there were a wave election coming we would have seen more signs of it by now. But political time is nonlinear and a lot of waves are late-breaking, especially in midterm years. Most forecasts issued at this point in the cycle would have considerably underestimated Republican gains in the House in 1994 or 2010, for instance, or Democratic gains in the Senate in 2006. (These late shifts don’t always work to the benefit of the minority party; in 2012, the Democrats’ standing in Senate races improved considerably after Labor Day.) A late swing toward Republicans this year could result in their winning as many as 10 or 11 Senate seats. Democrats, alternatively, could limit the damage to as few as one or two races. These remain plausible scenarios — not “Black Swan” cases.
Still, the most likely outcome involves the Republicans winning about the six seats they need to take over the Senate, give or take a couple.
Last week, Nate Cohn saw no electoral waves on the horizon:
The Republicans have a great opportunity to take back the Senate, even without an anti-Democratic wave. This year’s Senate contests are being fought on Republican-leaning turf. There are seven Democratic-held Senate seats in states won by Mitt Romney, more than the six needed to retake the chamber. There are also a handful of competitive races in presidential battlegrounds. These are contests the Republicans could win under neutral or even Democratic-leaning conditions.
But the Republican task will become much more difficult if there isn’t a G.O.P. wave. The distinguishing feature of this year’s Senate battleground is a broad and competitive playing field where, so far, the Republicans haven’t broken through. They haven’t yet locked down seats like Arkansas or Louisiana, where Democratic incumbents remain doggedly competitive in places where Mr. Romney won by around 20 points in 2012.
If there isn’t a Republican wave, this year’s Senate contest will devolve into the electoral version of trench warfare.
Sam Wang downplays Silver’s forecast:
At this point, Senate control comes down to as few as five* races: AK, CO, IA, KY, and LA. Think of these races as coin tosses. Then Democrats have to win 3 out of these 5 tosses to retain control. (I’m simplifying matters, but not by much.) These coins are not perfectly fair, and the overall situation is a little unfavorable to Democrats. That is basically the amount of uncertainty expressed in Silver’s probability.
Fundamentally, any probability in the 40-60% range is a numerical way of saying “I don’t know.” (Just to poke at the scar a bit, “I don’t know” is what Silver should have said when he intimated that Brazil would probably beat Germany in the World Cup. We all know how that turned out.)
Bernstein reacts to Silver’s forecast by emphasizing that “every seat counts in the Senate”:
[A] 51-49 Republican advantage is a very different situation than a 55-45 advantage (which is possible if everything breaks right for them). Similarly, a 50-50 Senate with Vice President Joe Biden breaking ties isn’t the same as he 53-47 advantage that strategists for the Democrats are still hoping for. Some of this is obvious: Getting one defection from the other party to win a vote is a lot easier than getting three. We know there are many things that Ted Cruz and Tim Scott enthusiastically support that would draw a dissent from fellow Republican Susan Collins. And there are plenty of things that Joe Manchin won’t join on no matter how much his fellow Democrats Barbara Mikulski or Tammy Baldwin want them.