Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

From President Obama to Bernie Sanders, Democrats are increasingly sounding the alarm on third-party candidates as polls show the Libertarian Party nominee Gary Johnson and the Green Party’s Jill Stein siphoning more support from Hillary Clinton than Donald Trump.

"If you vote for a third-party candidate who's got no chance to win, that's a vote for Trump,” President Obama said this week in a radio interview, echoing a message also made by his wife and other top Democrats on the stump.

Liberal super PACs are running -- and planning to run -- ads informing young voters that Johnson is at odds with them on many issues, while progressive groups are running massive canvas operations targeting liberals who might stay home or vote third party. Clinton’s campaign is officially keeping their distance, but surrogates have become more vocal in recent days.

The effort is targeted, purposeful and necessary, Democrats say. In an election where a fraction of a percent could determine if Clinton wins or loses, third-party candidates could play the spoiler -- as Democrats who lived through the 2000 election remember all too well.

The appeal of "none of the above" is obvious in a year when both major party nominees are disliked by so many. Endorsing Johnson Friday, the Chicago Tribute wrote that he's a "principled option" for a "dismayed, disconsolate America."

Stein is averaging about two percent in the polls while Johnson is seeing support from about eight percent of voters, but among millennials, their backing roughly doubles. Johnson received 17 percent support among voters under 35, according to the latest NBC/Wall Street Journal poll.

Much of that support is coming from former Bernie Sanders voters, survey data suggests. And since many of them don’t see Clinton and establishment Democrats as credible messengers, some of Sanders’ top backers have taken it upon themselves to speak out, turning former Clinton foes into allies.

“Gary Johnson and Donald Trump have one thing in common. They're frauds,” said Jonathan Tasini, who primaried Clinton when she ran for re-election in the Senate in 2006 and this year became a prominent Sanders surrogate. “They're both appealing to the unhappiness, despair and fear of a lot of Americans, but would actually make things worse.”

Johnson has appealed to young voters, many of whom are turned off by the two-party system, with a centrist message and appeals on marijuana legalization, civil liberties, and anti-interventionist foreign policy.

But progressives warn that he’s on the wrong side of just about every other issue Sanders-aligned young voters care about. Johnson supports: The Trans Pacific Partnership, fracking, the Keystone XL pipeline, cutting social safety net programs, and cutting the corporate tax rate to zero.

“I think that there should be unlimited campaign contributions, but that there should be 100 percent transparency,” he said in a MSNBC town hall this week, taking a radically different approach to the core issue of Sanders’ campaign. Johnson added that politicians should wear “NASCAR jackets with patches commensurate with the size of donations.”

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

And Johnson opposes: Major government intervention on climate change, tougher Wall Street regulations, the minimum wage, paid family leave, and Obamacare. Afterall, he’s a former Republican running as a Libertarian.

“If we followed his climate ‘policies’ and frack and pipeline the heck out of the country, we'll need all the weed we can find,” quipped Bill McKibben, the climate activist who founded 350.org and became a prominent Sanders ally.

NextGen Climate, a deep-pocketed pro-Clinton group, is putting money behind that message. The group has so far spent $100,000 telling young voters that Johnson thinks nothing should be done to address climate change - a position at odds with the majority of millennials who think the government should tackle the global problem.

“Thinking about voting for Gary Johnson?” the narrator asks in the opening of a digital ad playing online in five critical battleground states - Nevada, Ohio, Iowa, Pennsylvania and North Carolina. The ad then depicts Johnson as clueless and extreme.

“In billions of years the sun is going to actually grow and encompass the earth right?” Johnson says, downplaying the risk of climate change after promoting the expansion of coal.

Related: Jeb Bush: Not Voting for Clinton or Trump Would Send Message

“Millennials can determine the outcome of this election -- and we know that the more they learn the differences between the candidates on climate, the more they support Hillary Clinton,” said Jamison Foser, senior adviser for NextGen.

The League of Conservation Voters, another pro-Clinton environmental group, is doing similar work, but on the ground.

LCV is running persuasion campaigns hoping to reach 970,000 voters in three states - North Carolina, Pennsylvania and Nevada. With one of the largest ground game operations on the Democratic side, they say they are well prepared to attempt to convince a third party supporter to back Clinton.

“We find that you can successfully persuade people that vote for Johnson or that vote for Stein … that a vote for anyone other than Hillary Clinton is a vote for Donald Trump,” said Clay Shroers, LCV’s national campaigns director.

The Johnson campaign has been highlighting the progressives’ effort as proof that his campaign is effective.

“I guess when they see an outsider showing strength among millennials, independents, Hispanics, the active military and the LGBT communities, they get nervous,” the campaign wrote in a Facebook post.

Johnson and Stein have played up notions that Trump and Clinton are both part of the same corrupt duopoly, and a survey of millenials commissioned by NextGen found that nearly one-third of young voters don’t see major differences between the two major candidates.

But Adam Green, the co-founder of the Progressive Change Campaign Committee argues not supporting Clinton risks undoing all the work progressives have done to move her and the Democratic Party on key issues.

“Voting for Gary Johnson wouldn't just be throwing away a vote and possibly forfeiting a progressive governing moment in 2017 -- for progressives, it would be actively voting against your values on every economic issue,” said Green.

MoveOn.org, one of Sanders’ biggest backers, has been delivering a related message to members’ doors, email inboxes, and Facebook pages with a massive volunteer canvassing effort targeting progressives who might either stay home or vote for a third-party candidate.

The group found that the most effective message is a tactical one -- to argue that the only way to stop Trump is to vote for Clinton. Attacking Johnson or Stein directly can backfire, they found. “Anyone who is thinking about Johnson almost certainly is already adamantly opposed to Trump,” said Ben Wikler, the group’s Washington director.

Even the progressive groups prone to support third-party candidates are working to persuade their members and supporters that this year is not the year to do so.

Arisha Hatch, director of Color of Change PAC, a progressive group that works to engage people of color in electoral politics, said third parties are “critical to our Democracy,” but admits that this is not the year for voters to chose a third party.

“We’re also seeing is that this is not a business as usual election with what we’re seeing coming out of the right wing with Donald Trump,” Hatch said.

The Democratic Coalition Against Trump, a small-dollar super PAC but with a large social media presence, has slowly been changing their mission as Clinton struggles to solidify the millennial vote.

“I think we’re are probably going to make more of an effort to gently remind folks that Gary Johnson is not a viable alternative,” said Jon Cooper, chair of the super PAC.

Meanwhile, they’ll argue that Johnson is hardly the lesser of this years’ evils.

“Johnson will let people be stoned while he dismantles the country,” said Sanders supporter Tasini.