JACOBSON: A key reason why the Democrats have reason for optimism in 2016 is that they’re already kind of at rock bottom. You can only go up from there. Combine that with the fact it’s a presidential election year, so the turnout tends to be more Democratic, as opposed to midterm years.

But then the wildcard is Trump. It looked like a few weeks ago he’d be toxic all the way down the ballot, but recent polls are showing me that’s not the case anymore. I think we don’t know what the answer to that is; we have a lot way to go.

I did factor in the possibility that Trump could have a negative down-ballot impact in at least certain purplish states. So on the margins, that could help with Democrats. But really, fundamentally, it’s that Democrats are already in a bad position and can’t help but go up.