Vermont Senator Bernie Sanders will challenge Donald Trump for president in 2020. Thanks to popular (rather than merely "populist") policies, and a strong primary run in 2016 against a Democratic party apparatus that did everything it could to stop him, he becomes an instant front-runner. "We began the political revolution in the 2016 campaign, and now it's time to move that revolution forward," the independent senator told Vermont Public Radio in an interview airing Tuesday morning.