In this Sept. 3, 2016 file photo, Libertarian presidential candidate Gary Johnson speaks during a campaign rally in Des Moines, Iowa. - Photo by AP Photo/File / Scott Morgan

NEW YORK -- Gary Johnson's standing in polls isn't enough to get him into the presidential debates, but it's enough to complicate the race for the White House.

Photo by Tae-Gyun Kim / AP Photo

Green Party presidential candidate Jill Stein speaks during a news conference at South Austin neighborhood Thursday, Sept. 8, 2016, in Chicago.

The unpopularity of both Republican Donald Trump and Democrat Hillary Clinton has opened an opportunity for third-party candidates, and pollsters say Johnson, a Libertarian who will be on the ballot in all 50 states, is pulling slightly more support from Clinton than Trump. The question now is whether Johnson will sustain that, or whether his support will fade as voters take a serious look at their choices.

"In any other year, I'd say that the safest prediction would be to take Johnson's current average of 8 percent and cut it in half by Election Day, giving him about 4 percent when everything is said and done, but it's not a conventional year," Democratic strategist Craig Varoga said via email.

Johnson serves as a reminder that two essential components of the coalition that elected President Barack Obama -- young voters and independents -- aren't necessarily happy with Clinton or with Trump.

"We've found in our surveys that [Johnson's] presence hurts Clinton more than it hurts Trump, and the fact that he did not backslide after Aleppo means that he is possibly here to stay," said Tim Malloy, assistant director at the Quinnipiac University poll, referring to a Sept. 8 television interview in which Johnson seemed not to know about the besieged Syrian city.

In a national Quinnipiac poll released Wednesday, Clinton led Trump by more than the margin of error in a head-to-head matchup. But when Johnson and the Green Party's Jill Stein are included, Clinton's lead shrinks to within the margin of error, according to the poll.

A New York Times/CBS News national poll released Thursday also showed Clinton's lead shrinking when third-party candidates were included. Among likely voters, Clinton leads in a head-to-head matchup. With Johnson and Stein included, Clinton and Trump are tied, according to the poll.

While Stein, who has made appeals to disenchanted supporters of U.S. Sen. Bernie Sanders of Vermont, is much more likely to eat into Clinton's support than Trump's, she hasn't consistently performed as well in national polls as Johnson. And, unlike Johnson, she won't be on the ballot in all 50 states, including Nevada and North Carolina, two battlegrounds Clinton hopes to win. In the last nine presidential elections, Nevada has consistently voted for the overall winning candidate, while North Carolina has voted for the Republican nominee eight times.

Johnson currently averages 8.3 percent in national surveys, according to the Real­ClearPolitics' polling average, well below the 15 percent threshold for inclusion in the three scheduled presidential debates. Johnson and his running mate, former Massachusetts Gov. Bill Weld, have made a recent push for inclusion in the debates, including a full-page ad in Wednesday's New York Times.

"An important thing for Johnson would be to theoretically get into the debates, but that looks almost impossible at this point, which might make his voters less sticky," said Geoffrey Skelley, a political analyst at the University of Virginia's Center for Politics.

For third-party candidates, the biggest hurdle historically has been getting voters to take them seriously. As an election draws closer, voters tend to engage in what University of Denver political science professor Seth Masket calls "strategic voting."

"Voters come to realize that they really have a choice between two candidates that have a shot, and if they vote for anyone else, they're not only wasting their vote but making it more likely that the candidate they like least will win," Masket said.

Masket said he doesn't expect Johnson to swing the election one way or the other, but his support shows that there's a portion of the electorate having a hard time rallying behind either Clinton or Trump. "The real difference this year is that you have two historically unpopular major-party nominees," he said.

Though Johnson may draw some comparisons to the Green Party's Ralph Nader, whom some blame for costing Democrat Al Gore the 2000 election by pulling votes in Florida and New Hampshire, Johnson's effect on Clinton's numbers is less lopsided.

In 2000, Gore lost Florida to George W. Bush by 537 votes after a recount. Nader got 97,488 votes in Florida -- about 1.6 percent of the total in the state. Even though Gore won the popular vote nationally by more than 500,000 votes, Florida's 25 electoral votes put the Republican over the top in the Electoral College.

Murray said that based on his own polling, Johnson and Stein tend to cut Clinton's margin against Trump by just 1 percentage point.

"If Trump wins [a state] by 2 points, I would say it's very unlikely that Johnson cost Clinton that state," he said.

Clinton's bigger problem is a lack of enthusiasm from younger voters, some of whom are defaulting to Johnson and Stein, according to recent polls.

In Wednesday's Quinnipiac poll, Clinton's support among people ages 18-34 dropped from 55 percent to 31 percent when Johnson and Stein were included.

Clinton's campaign recognizes the problem. Clinton is planning an event Monday in Philadelphia explicitly to emphasize "the stakes of the election for millennials." Sanders and U.S. Sen. Elizabeth Warren of Massachusetts both will be campaigning on the same theme today in Ohio.

"This is an audience in particular that grew up after Bill Clinton was president, and we believe there's a lot they can learn about her and about the stakes in this election," said Jennifer Palmieri, the campaign's communications director. "It's going to be a priority for us and our surrogates."

For now, third-party supporters feel safe continuing to voice their discontent by backing Johnson, Skelley said.

"Obviously the race has narrowed, but if you're looking at the Electoral College map, Clinton still leads in all the states she needs to get over 270 electoral votes," Skelley said. "The real question is are they going to stay with Johnson if the race gets on a knife's edge."

Information for this article was contributed by Margaret Talev of The Associated Press.

A Section on 09/17/2016