Democratic former vice presidents including Hubert Humphrey, Walter Mondale, and Al Gore haven't had much success running for president—but Gore hopes Joe Biden will be able to break the streak. Gore tweeted his endorsement of Biden ahead of an Earth Day event Wednesday, the New York Times reports. "If I was talking to one person who had not yet decided who to vote for in this upcoming election, I would just say plainly and simply: This is not complicated," Gore said at the virtual town hall. "If you care about the climate crisis, if you want to start solving the climate crisis, this is not rocket science." He said he would tell the undecided voter that President Trump "is the face of climate denial globally," the Hill reports. (Barack Obama endorsed Biden last week.)