Supporters of Sen. Bernie Sanders (I-Vt.) rally in New York City's Washington Square Park in April. His spirited presidential campaign resonated with young and liberal voters. (Spencer Platt/Getty Images)

Millennials are souring on Hillary Clinton. Again.

Not that they were ever so sweet on her to begin with, at least relative to how they swooned over other Democrats. Both Bernie Sanders in the recent primary campaign, and Barack Obama in the 2008 and 2012 general elections, received far more love from young voters. But in any case, Clinton’s already weak millennial support has gotten much weaker in the past month.

Still, there’s good reason to believe they’ll come around, even if they do so grudgingly.

First, the data. Several new polls suggest young voters — a low-turnout but nonetheless key component of the Democratic coalition — are abandoning Clinton in droves.

Quinnipiac, for example, found last month that Clinton had a big fat 24-point lead over Donald Trump among 18-to-34-year-old voters (48 percent to 24 percent). Now that margin has shriveled to just five percentage points (with Clinton at 31 percent, Trump at 26 percent).

Nationwide Fox News polls of registered voters also found that Clinton’s lead has narrowed to nine points, from 27 points in late July and early August. And a USC Dornsife/Los Angeles Times national poll has Clinton’s August lead not only disappearing but reversing, with Trump now ahead among millennials by six points. There were outliers, but the trend was clear.

Polls in battleground states have likewise shown Clinton’s lead among millennial voters shrinking. In Michigan, for example, Clinton’s 24-point August lead among young voters has shriveled to just seven points. Clinton has just 31 percent of the youth vote there, compared with Trump’s 24 percent.

In most of these polls, the young supporters ditching Clinton seem to be shifting not to Trump but to third-party candidates, particularly Libertarian Gary Johnson. The Michigan poll has Johnson tied with Trump; the national Quinnipiac poll actually has Johnson slightly ahead of Trump among under-35 voters.

These trends have been met with liberal teeth-gnashing and garment-rending, plus a lot of sanctimonious scolding of Kids These Days. How dare these ungrateful young hooligans turn their backs on the only serious candidate who actually cares about their issues! Are they really too young to remember the horrors that resulted when Ralph Nader played the spoiler in 2000? Quoth one columnist, “I know you’re young, but grow up!”

The Clinton campaign seems to have gone into emergency millennial mollification mode, too.

That means a flurry of college visits, including from progressive heartthrobs such as Sanders, Elizabeth Warren and Michelle Obama. The Clinton campaign explicitly advertised these events as an appeal to prodigal young voters.

The surrogate speeches haven’t always gone according to plan, though. Obama’s speech at George Mason University was at one point met with chants of “four more years”; her stumping apparently got the crowd pumped for the wrong politician.

The Clinton campaign has thus also been desperately seeking coverage in millennial-tailored media. She whipped up an inane essay for Mic titled “Hillary Clinton: Here’s What Millennials Have Taught Me.” (The tl;dr lesson: Millennials are totes awesome.) And she sat for an awkward, if amusing, interview on “Between Two Ferns” with actor Zach Galifianakis.

In my view, all the kvetching, cajoling and clowning around in the world are unlikely to move young voters. But you know what might? Numbers.

Several recent polls, anyway, suggest that younger voters are much more likely to see a Clinton presidency as a fait accompli. Per Quinnipiac, 71 percent of voters younger than 35 believe Clinton will win in November; just 49 percent of voters older than 65 believe the same. YouGov also finds that 58 percent of voters under 30 expect a Clinton victory, versus 47 percent of those over 65.

If you believe a Clinton presidency is inevitable, then casting a ballot for a third-party candidate probably doesn’t feel like it has much consequence. It’s a mere protest vote, a victimless expressive gesture, like angrily tweeting into the void, kneeling during the national anthem or, I don’t know, sending unhinged hate mail to unsuspecting columnists.

But a tighter race — one, ironically, made tighter largely because of millennial defections from the Clinton camp — changes the calculus. It’s riskier to “throw away” your vote, either by supporting someone who has no chance of winning or by abstaining from the polls altogether.

See, millennials may not adore Clinton, but they really, really hate Trump. Six in 10 young voters view him “strongly” unfavorably, and the same share describe him as “racist.” Don’t be surprised if their third-party crushes start to fade as the prospect of President Trump begins to feel all too terrifyingly real.