Lots of third-party voters assume Clinton will win. That could throw the race to Trump.

Third-party candidate Gary Johnson, the Libertarian from New Mexico, is doing better than most minor party candidates do at this point in a presidential election — he’s currently pulling about 8 percent of the vote in national polls.

One apparent reason for this — as outlined by Harry Enten at FiveThirtyEight and Matt Yglesias here — is that Donald Trump and Hillary Clinton are two uniquely unpopular candidates. In other words, voters hate the leaders of the major parties so much that the idea of casting a ballot for the “lesser of two evils” candidate is too much an ask for some of them.

But there seems to be another factor in play, as YouGov pollster Will Jordan pointed out on Twitter: Far more third-party and undecided voters think Clinton will win than think Trump is going to win. Fully 50 percent of those voters say they think Clinton will win, while only 15 percent say they think Trump will (with the rest unsure).

This point supports another theory behind Johnson’s relatively strong performance so far, as Andrew Gelman, a statistician and political science professor at Columbia University, shared with me in August:

“Perot in 1992 received 19 percent of the vote but won zero states. That election was not close, which perhaps made people feel more free to vote for a third party. I’d guess that the opportunity for third-party success in 2016 is again if the election does not seem like it will be close,” Gelman said.

Back in August, Clinton had a comfortable lead over Trump. But now that the polls have narrowed — some even have Trump leading in key swing states — it’s possible these voters will start thinking their votes really matter again, and will choose a major party nominee.

But if the sentiment that a third-party candidate vote doesn’t matter persists, it could pose a particular challenge for Clinton. She is very unpopular, but voters have also generally assumed she’ll win, as Vox’s Matt Yglesias explains:

If polls stay very tight or Trump pulls into a lead, then anti-Trump messaging to Johnson and Stein voters could take the form of classic warnings about spoilers and wasted votes.

But the fact that Clinton has been consistently leading in the polls — and in August was doing so by a large margin — has itself undercut purely tactical arguments for voting Clinton. If she is overwhelmingly likely to win, which is what people have been hearing, then you may as well not vote for her if you don’t like her.

It’s simply going to be very hard for Clinton to open up the kind of stable lead that her supporters think Trump’s awfulness deserves while she herself is so little-liked. September of a general election year is probably not a great time to turn that around.

But the fact remains that her basic problem in this race is almost painfully simple. Over the course of her winning primary campaign she became a deeply unpopular figure. And it’s hard — indeed, unprecedented — for such an unpopular person to win the presidency.