A new report from FiveThirtyEight states that it’s extremely unlikely that the Democrats are going to win control of the Senate. The House is another story, for that matter. It’s expected that Republicans are going to lose control based on polling predictions, but as we saw in 2016, that doesn’t necessarily mean people will vote that way.
At the same time, Republicans have a fairly clear advantage in the Senate (as Democrats do in the House) — clearer than the edge Hillary Clinton had before the 2016 election, when President Trump had roughly a 3 in 10 chance to win the Electoral College. In 2016, a normal-sized polling error (if it worked in Trump’s favor) was probably going to be enough to give him a victory in the Electoral College. And that’s exactly what happened: The polls weren’t great in 2016, but they were about as accurate as they have been on average since 1972. Because the race was close and because Clinton was underperforming in the Electoral College, a small and routine but systematic polling error was enough to give Trump the win.
The difference this year is that a normal-sized polling error in Democrats’ direction would merely make the race for the Senate close. (Likewise, a normal-sized polling error in the GOP direction would make the House close, but Republicans would still have to fight it out on a district-by-district basis.) A sports analogy, for those so inclined: In 2016, Trump was doing the equivalent of driving for the game-winning touchdown with the odds somewhat but not overwhelmingly against him. If enough undecided voters in the Midwest broke toward him, he was going to win the Electoral College. In the Senate this year, by contrast, it’s more like Democrats are driving for the game-tying touchdown; they still have to win in overtime even if they score.
Nate Silver, the author of the piece, also outlines some problems Democrats have to overcome to win including no clear path to victory and winning in races where they’re underdogs or barely favored to win in the first place.