Tuesday, September 16, 2014

Decreasing robustness in the Republicans' path to victory

We use the word "robust" to describe things that still perform very well even when some of the basic assumptions behind it are violated. For example (and the word generally isn't used to describe them), cockroaches are pretty robust with regard to the environment, if the well-touted factoid that cockroaches can survive a thermonuclear blast carries any weight. No matter what environment we put them in, they're incredibly hardy survivalists.

With that in mind, we now say that the Republican path to control of the Senate is considerably less robust than it was a couple months ago. 

What does it mean when we say that path was robust back in July or June? It means that there were so many paths that only the biggest of screw-ups on multiple fronts would cost them the chamber. Republicans then had (and still do have today) pretty much surefire pickups in Montana, South Dakota, and West Virginia. Races in Arkansas and Louisiana were leaning their way, Democratic incumbents in North Carolina and Alaska were defending total toss-ups, and races in Colorado, Iowa, and Michigan were competitive enough that they had at least a one-in-three chance of winning them. Meanwhile, Minority Leader Mitch McConnell's seat in Kentucky was gradually trending back toward him after several months of momentum toward his Democratic challenger, and Georgia was still pretty much a toss-up. There was a clear path toward at least a five-seat gain (MT, SD, WV, AR, LA) and only one more out of the many lower-hanging fruits would give them the Senate. I gave them about a two-thirds chance of winning the Senate.

A lot's changed since then. True, Sen. McConnell has shored up his defenses in Kentucky; Republicans have placed a lock on Montana with the withdrawal of incumbent Sen. John Walsh from the race, and the races in Iowa and New Hampshire have loosened up a little for the moment following the primaries. But Democrats have made stronger and more important gains. In Arkansas and Louisiana, Democratic incumbents have tipped the race ever so slightly closer to the middle; in Michigan they've increased their lead, and in North Carolina and Colorado the incumbents have very clearly pulled ahead of their Republican challengers.


The map highlights states where the odds I give have changed dramatically since the June 30 ratings update. You can see that Republicans have made gains in just as many states as Democrats have. The difference, however, is that while some Republican gains have been in "likely Republican" (Montana) or "likely Democratic" (New Hampshire) states, the Democratic gains have all been in leaners and toss-ups. Those are the states where changes in probabilities are important. In Montana, for example, the change from 94% Republican to 99%+ Republican didn't do much to Republican chances of taking the chamber. The Montana lock remained a Montana lock.

However, in June, North Carolina was at a total toss-up (very very slightly leaning toward Speaker Thom Tillis). If we ordered the states from safest Republican (Alabama) to safest Democrat (Hawaii), we'd see that North Carolina in June was the sixth-likeliest Republican pickup--six of course being the number of seats Republicans need to win the Senate. You could say that North Carolina was the seat that gave Republicans the chamber (although that's about as meaningful as saying one particular senator was the "60th vote" against Obamacare). But as Sen. Kay Hagan has gone from slightly trailing Speaker Tillis to opening up a fairly comfortable lead, North Carolina gradually lost its status as that magic sixth seat. It took away one solid chance at a Republican pickup.

Colorado, Arkansas, and Louisiana have similar stories. In Arkansas and Louisiana, Democratic chances have only very slightly improved--but in states as important as those two, a slight improvement in their chances means an improvement across the board in their chances of holding the Senate. In some competitive states--notably Georgia--Republicans have improved their chances. But in most of the others it's Democrats who've done the same. It probably also doesn't help that Sen. Pat Roberts is now in hot water in Kansas. Republicans have a lot less room for error now than they did before.

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