This implies two crucial points. First, the seats that the GOP is defending this cycle are seats that it has typically won even when it is losing overall. In some places, such as Arizona, Tennessee, and Texas, that is due to the natural partisan tilt of the states. In Nevada, it is due to the fact that Heller is well known and a good fit for the state.

Second, the Democrats are defending seats that, to be honest, they have no real business holding in the first place. Republicans really botched their comeback effort in 2012, which yielded needless losses for the GOP in Indiana, Missouri, Montana, and North Dakota. Luck, such as it is, has consistently been on the Democratic side with Senate Class 1 for many cycles. But this time it doesn’t seem to be favoring the Democrats as much. That leaves them more vulnerable than they would be with any other Senate class.

None of this is to suggest that the Kavanaugh effect is not real. It is just to serve as a reminder that Senate elections are only a dim or distorted picture of public opinion. That was by design, as the Framers of the Constitution originally gave the power of selecting senators to state legislatures. But even after the passage of the 17th Amendment, which mandated popular elections for all senators, we still see the upper chamber’s strange relationship to public opinion. President Donald Trump is unpopular, and his Republican party looks likely to lose a substantial number of seats in the House, which was designed to reflect public opinion. But thanks to the peculiarities of the Senate classes, the GOP may walk away from the November midterm having netted a seat or two in the upper chamber.