Former Vice President Al Gore is hitting the campaign trail, and will try and use his favorite issue to convince young people to support Democratic presidential nominee Hillary Clinton.

Gore, 68, has been on the sidelines most of this election cycle, despite serving as former President Bill Clinton’s two-time running mate. Gore didn’t endorse Clinton until the Democratic convention in July, which he did not attend.

Clinton hopes Gore will use his global warming credentials to rally millennials around her campaign. Clinton’s struggled to gain traction among younger voters, but hopes their concern about global warming will convince them to vote against Republican presidential nominee Donald Trump.

Global warming is not a major issue for most voters, but The Washington Post notes “it ranks higher among millennials.” Gore is working out the details on how he can bring more young people into the Clinton camp, according to the Post.

Gore has already warned disaffected Sen. Bernie Sanders supporters to not vote for a third party candidate.

“First of all I understand their feelings and misgivings,” Gore told ThinkProgress in August. “But if they are interested in my personal advice. I am voting for Hillary Clinton. I urge everyone else to do the same.”

“I particularly urge anyone who is concerned about the climate crisis, sees it as the kind of priority that I see it as, to look at the sharp contrast between the solar plan that Secretary Clinton has put forward, and her stated commitment to support the Clean Power Plan, and the contrast between what she has said and is proposing with the statements of the Republican nominee, which give me great concern,” Gore said.

“I would also urge them to look carefully, as I know they have, at the consequences of going in another direction for the third or fourth alternative,” he said. “The harsh reality is that we have two principal choices. And I am supporting Hillary Clinton.”

Democrats have been trying to use global warming as a major issue to get young people out to the polls. In fact, liberal billionaire Tom Steyer has made it his mission.

Steyer’s group NextGen Climate Action is working to increase turnout among young voters who care about global warming.

NextGen has even implored young people to not vote for Libertarian nominee former New Mexico Gov. Gary Johnson.

A vote for Gary Johnson-and his belief that we should do nothing about climate change-is a vote for Trump. pic.twitter.com/x4vQ6lUYts — NextGen Climate (@NextGenClimate) October 2, 2016

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