A Quinnipiac University poll Wednesday became the latest to highlight a weak spot for Democrat Hillary Clinton — third-party candidates hurt her more than they hurt Republican Donald Trump.

In a head-to-head matchup, Clinton leads Trump nationally by 5 percentage points, 48 percent to 43 percent.

Trump’s support among millennials drops by just 8 points from his two-candidate share, while Clinton loses 24 points.

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But when other candidates are included, Clinton’s lead over Trump shrinks to 2 points. Libertarian Gary Johnson, who celebrated this week that his name will appear on the ballot in all 50 states, captures 13 percent of the vote in the Quinnipiac survey. Green Party candidate Jill Stein, meanwhile, gets 4 percent in the poll.

“It hurts Hillary Clinton more than it hurts Trump,” said Tim Malloy, the poll’s assistant director. “There’s such huge dissatisfaction with both Trump and Clinton … They have just so appallingly bad from-the-gut numbers.”

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Johnson and Stein both perform disproportionately well among younger voters, which is the likely source of Clinton’s problem. With Trump stunningly unpopular among millennial voters, and younger voters tending to lean heavily Democratic anyway, they tend to choose Clinton if they have no other option. Given other choices, though, many take them.

Johnson actually out-polls Trump among voters younger than 35, 29 percent to 26 percent, and trails Clinton by only 2 points. Trump’s support among that group drops by just 8 points from his two-candidate share, while Clinton loses 24 points.

Johnson also gets 19 percent support from voters 35 to 49 years old, but his support drops to single digits among older voters.

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Even the head-to-head numbers represent a weakening of Clinton’s position in August, when Quinnipiac found she had a 10-point lead over Trump.

Malloy said third-party candidates tend to perform worse on Election Day than they do in polls — perhaps as people initially inclined to cast a protest vote worry about casting a ballot for a candidate who cannot win.

But Malloy said it is not clear the historical pattern will hold, given how poorly Americans rate both Trump and Clinton.

“When you get to that point, all bets are off,” he said. “We are rewriting the book this time around. It’s hard to say.”

Carla Howell, political director with the Libertarian Party, pointed to an analysis by statistics guru Nate Silver’s FiveThirtyEight website indicating that Johnson is showing more staying power than other third-party candidates.

“He may be a big departure from the trend you cited,” Howell said.

Johnson’s 13-percent showing puts him close to the 15 percent threshold Johnson needs to meet in five major polls in order to be included under the rules set by the Commission on Presidential Debates.

“Given the growing interest and support of the Johnson-Weld campaign, voters deserve to hear Gary Johnson on the presidential debate stage,” campaign manager Ron Nielson said in a prepared statement.

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Howell argued that it is not too late for Johnson and his running mate to make the debates.

“It’s definitely doable, especially with a couple key players on the CPD calling for inclusion and a tremendous amount of popular support for including Gov. Johnson and Gov. [William] Weld,” she said.

How Johnson’s inclusion in the debates would impact the overall race is impossible to predict. But to understand the importance of young voters to Clinton, consider President Obama’s showing among that bloc in 2012. According to exit polls, he won 60 percent of voters younger than 30, and they made up nearly a fifth of the electorate.

Clinton needs young voters to participate in strong numbers and to ditch Johnson and Stein — else they may cost her the election.

Howell argued that young voters are attracted to Johnson’s stands on views like marijuana legalization, opposition to government surveillance, gay marriage, and ending foreign intervention. She acknowledged that dissatisfaction with the major-party candidates is playing a role.

“It’s clearly both,” she said. “Sixty-five million voters in this country believe Gov. Johnson lines up with their views on the issues … Young voters see him as working for their interests, as do increasing numbers of all Americans.”