ABC's Ryan Struyk noticed something interesting in the new Post-ABC poll.

I'll stipulate at the outset that most definitions of "millennial" extend to people who are up to 35 or so and also that the definition of "millennial" is variable and generally poorly defined. I'm using "millennials" here to mean "youngish people." Or, really, "youngish people who can be described with a term that people like to click on."

Back to Struyk's point: Yes, 41 percent of those age 18 to 29 say that they are certain to vote, with an additonal 15 percent saying they'll probably vote. Older voters are much more likely to say they're committed to going to the polls. Here's the breakdown from the poll, including all respondents.

The darkest red bars are the ones to which Struyk refers.

But that's everyone, including people who aren't registered to vote. People who aren't registered to vote are obviously less likely to vote, and younger Americans are more likely not to be registered. (A lot of reasons: jobs with unusual hours, moving and not updating registration, etc.)

If we look only at registered voters, younger people are still less likely to say they're certain to vote than older ones, but by a smaller margin. They're also more likely to say they're certain to vote this November than 18-to-29-year-olds were to say it in 2012. Now, nearly two-thirds of registered voters under 30 are certain to vote, compared with 54 percent four years ago.

A critical note at this point: The number of respondents in the poll who are under 30 was relatively small, meaning that the margin of error was bigger. So the bars on these charts are a bit hazier than they might look.

For example: If we compare how that age group planned to vote in late September of 2012 and 2016, there's a huge gulf. In the most recent survey, voters under 30 preferred Democratic nominee Hillary Clinton by only 2 points (again, with a wide margin of error) compared with a 30-point preference for President Obama four years ago.

(Remember that young white voters vote more like whites overall than they do like younger voters overall.)

That narrow margin is in a head-to-head contest, though. When you switch to a four-way contest, Republican nominee Donald Trump loses a lot more support from younger voters than Clinton does. Her lead is still only 7 points, but that's better than 2 points.

This is the problem for Clinton. There's a big margin of error, sure — but that narrow lead with younger voters should be inspiring more worry than whether or not they turn out. Winning an election takes both support and a cast ballot. At this point in 2012, Obama was doing far better on the former point and slightly worse on the latter. Clinton is currently stumping with Sen. Bernie Sanders of Vermont, millennial-whisperer, to try to shift the support columns. Remember: Even with those numbers, Clinton and Trump are still tied in the new Post-ABC polls. She doesn't need Obama-style numbers with young voters; John Kerry only won them by 9 points (though, of course, he lost).

But she needs to build on the 44 percent support she gets from voters under 30 more urgently than she needs to build on the 41 percent who say they plan to vote.