Three Rust Belt swing states are critical to winning the presidency this year — Wisconsin, Michigan and Pennsylvania. In Pennsylvania, there is one issue that could be decisive: fracking natural gas. Opposition to fracking could be fatal for a candidate in the state, yet front-runners for the Democratic nomination have committed to banning fracking nationwide if elected. We went to western Pennsylvania, where fracking affects residents daily, to see whether electability in the state could really be reduced to this single issue. Guests: Shane Goldmacher, a national political reporter for The New York Times, traveled to Pennsylvania with Andy Mills and Monika Evstatieva, producers for “The Daily.” For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: Our investigative team revealed how immense amounts of methane, the primary gas acquired by fracking, are escaping from oil and gas sites nationwide, worsening global warming.What is fracking? And why is it so harmful to the communities that come in contact with the toxins it leaves behind?