So could Trump actually finish behind Johnson — or even take less of the youth vote than the two top third-party candidates, as the Q poll suggests?

It’s possible. But we’re dealing with small subsamples with large margins of error here. In addition, earlier polls with age-demographic data don’t show Trump struggling quite so much. A Washington Post-ABC poll showed Trump leading Johnson and Stein 32-11-7 (though the sample there was voters aged 18-39), and Monmouth University last month showed Trump at 30, Johnson at 14 and Stein at 6 among voters 18-34. Still not great numbers for Trump, but not quite as bad.

It’s also generally true that third-party candidates poll better than they perform on Election Day, when voters might opt for someone who has a much better chance of actually winning. American politics is a two-party system for a reason.

It’s also not clear that all or even most of Johnson’s support comes at Trump’s expense.