In recent elections, more and more voters have been choosing candidates from the same party for president and Senate. That trend appeared to be holding true this year too, even with Donald Trump, unusual as he is, on the ballot. So as Hillary Clinton jumped out to a bigger lead in the polls starting after the first presidential debate in late September, we might have expected Democratic Senate candidates to poll better as well. That hasn’t happened — the chance of Democrats controlling the Senate is only 54 percent in our polls-only model and 56 percent in our polls-plus model. CONT.
Harry Enten, FiveThirtyEight