This week, a historic case has landed in a Montana courtroom. A group of young environmentalists is suing the state, arguing that its embrace of fossil fuels is destroying pristine environments, upending cultural traditions and robbing young residents of a healthy future. David Gelles, a climate correspondent for The Times, explains why the case could be a turning point, and what a win in Montana would mean for the future of the climate fight. Guest: David Gelles, a climate correspondent for The New York Times.