Why Republicans Have a 55 Percent Chance of Retaking the Senate

We’ve updated the Upshot’s Senate model, which we call Leo, with the results of Tuesday’s elections in North Carolina. Thom Tillis, the State House speaker, won the Republican Senate primary there.

Leo was expecting Mr. Tillis to win. Before the election, Leo gave him an 86 percent chance of winning the nomination, either last night or in a July runoff. That number was based on polls and fund-raising data. Primaries can be volatile, so we think of these estimates more like very rough guesses than a proper model.

But because...