Democrats panicked by third-party candidates drawing support away from Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE are ramping up their attacks against Gary Johnson Gary Earl JohnsonWhat the numbers say about Trump's chances at reelection Presidential race tightens in Minnesota as Trump plows resources into state The Hill's Campaign Report: Biden condemns violence, blames Trump for fomenting it l Bitter Mass. primaries reach the end l Super PAC spending set to explode MORE and warning that a vote for a third party is a vote for Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE.

Liberal groups are passing around embarrassing videos of Johnson and running ads against him warning about his positions on issues like climate change that are important to young voters and independents.

ADVERTISEMENT

The Clinton campaign will rely heavily on Sen. Bernie Sanders Bernie SandersJacobin editor: Primarying Schumer would force him to fight Trump's SCOTUS nominee Trump campaign plays up Biden's skills ahead of Cleveland debate: 'He's actually quite good' Young voters backing Biden by 2:1 margin: poll MORE (I-Vt.) in the coming weeks as it seeks to shore up its deficit among young voters and left-leaning independents who are not energized by her campaign and are considering casting a vote for either Johnson or Green Party nominee Jill Stein.

The Libertarian ticket of Johnson and Bill Weld is running surprisingly strong among young voters — a cog in the Obama coalition that Democrats need to turn out for Clinton if she’s to pull away from Trump.

Whether Clinton reaches those voters could determine the outcome of critical battleground states like Colorado, Nevada and Pennsylvania.

Democrats still vividly remember the 2000 election and blame Ralph Nader for costing Al Gore Albert (Al) Arnold GoreCruz says Senate Republicans likely have votes to confirm Trump Supreme Court nominee 4 inconclusive Electoral College results that challenged our democracy Fox's Napolitano: 2000 election will look like 'child's play' compared to 2020 legal battles MORE the presidency in the closest election in history. They’re worried history could repeat itself in 2016, as third-party candidates are attracting more interest than they have in decades.

The Clinton campaign and its liberal allies are increasingly taking the threat from Johnson and Stein seriously, making direct appeals to young voters and punching down at the third-party candidates they view as potential spoilers.

“Young voters are suggesting that they’re uncomfortable with Clinton and are using Johnson and Stein as protest votes,” said Douglas Schoen, a former official in the Bill Clinton William (Bill) Jefferson ClintonGOP brushes back charges of hypocrisy in Supreme Court fight Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE administration. “The campaign must make the case that unless young people vote for Clinton, they’re effectively voting for Trump.”

NextGen Climate, the group run by liberal billionaire and environmental activist Tom Steyer, is on the ground in eight battleground states with a message that is almost exclusively aimed at reaching the millennial voters who are energized by the issue of climate change.

Last week, the group threw six figures behind digital ads mocking Johnson as a climate change denier and warning millennials that climate change will cost them trillions of dollars.

A source at NextGen told The Hill the group will be looking to turn out young voters for Hillary Clinton and down-ballot Democrats with a texting campaign in the battleground states and a carpooling service that will drive them to the polls.

The Libertarians have also attracted the ire of a group called ShareBlue, which is owned by longtime Clinton ally David Brock. The unabashedly pro-Clinton, for-profit media company has a strong following in the realm of progressive social media and has been using its platform in part to hammer Johnson as a flaky Republican.

ShareBlue CEO Peter Daou, a veteran of John Kerry John Forbes KerryThe Memo: Warning signs flash for Trump on debates Divided country, divided church TV ads favored Biden 2-1 in past month MORE’s and Clinton’s past presidential campaigns, told The Hill he’s targeting Johnson and Weld from the policy side and making the case for why their platform should be anathema to progressives.

Daou's website is also targeting Stein, who is pulling support from the far left. A recent post argued that Johnson and Stein "are not serious candidates."

Johnson and Weld hold liberal views on issues like marijuana legalization, abortion rights and non-interventionist foreign policy that have helped them gain traction among some young voters.

But both former Republican governors tend to hew closer to the conservative orthodoxy on issues like taxation, minimum wage, Social Security and Medicare, environmental regulation, and school choice.

“What we are trying to argue here is these are not the options you think they are,” Daou said.

That message is being amplified on social media by liberal celebrities like Cher, George Takei and Seth McFarlane, as well as some of the nation’s most prominent liberal writers, who are seeking to shame young voters away from the Libertarian ticket or warn that it could lead to a Trump presidency.

“I’d like to make a plea to young Americans: your vote matters, so please take it seriously,” Paul Krugman wrote in a Libertarian takedown in The New York Times last week.

In many cases, young voters and independents are not considering voting for Trump, the Republican nominee.

But they’re also not enthusiastic about voting for Clinton and appear to be attracted to the same outsider appeal of the Libertarians that once had them flocking to Sanders rallies.

“I think there’s a great deal of dissatisfaction among … young people, in particular with status quo establishment politics, and the two third-party candidates are coming across as not being part of the establishment,” Sanders said on MSNBC on Monday night, as he urged young voters to look at Clinton’s positions on climate change and college cost.

Sanders could ultimately be the campaign’s secret weapon. He drew young voters by the tens of thousands during the Democratic primaries and revealed on Monday that he’s plotting a “very, very vigorous” campaign schedule for Clinton.

The Clinton campaign isn’t putting any money behind its anti-third-party message yet. But vice presidential nominee Tim Kaine Timothy (Tim) Michael KaineTrump meets with potential Supreme Court pick Amy Coney Barrett at White House Names to watch as Trump picks Ginsburg replacement on Supreme Court Barrett seen as a front-runner for Trump Supreme Court pick MORE raised the specter of the Libertarians as spoilers in an interview with Yahoo’s Katie Couric last week, arguing that there never would have been a war in Iraq if Nader hadn’t cost Gore the election.

“Casting a vote, a protest vote, for a third-party candidate that’s going to lose may well affect the outcome,” Kaine warned. “It may well lead to a consequence that is deeply, deeply troubling. That’s not a speculation — we’ve seen it in our country’s history.”

There are several battleground states where it appears the third-party effect is working against Clinton.

A CNN-ORC survey that showed Trump with a 1-point edge in Colorado found Johnson and Stein combining for 30 percent support among those under the age of 45.

In Monmouth University polls of Nevada, Clinton once had a 5-point lead over Trump based on her strength among independents. The latest survey found Trump moving into a 2-point lead as independents moved away from Clinton into Johnson’s column.

And one eye-popping Christopher Newport University survey of Virginia found Clinton taking 34 percent among voters aged 18 to 34, followed closely by Johnson at 27 percent. Clinton still leads by 6 over Trump in that poll but only pulls 39 percent support overall.

Liberals interviewed by The Hill aren’t in full panic mode yet. Some are more concerned that the lack of enthusiasm is what could doom Clinton, rather than voters actually turning out for Johnson or Stein.

“The real risk is voters that should stand with Democrats and progressives in this election will not show up,” said Democracy for America spokesman Neil Sroka. “That’s why a proactive, positive-issues campaign is so important — we need to give people a reason to vote for the Democrats.”