The so-called megadrought that is afflicting the American West is the worst in 1,200 years, according to a study published this week. It has dried up water supplies, threatened ranchers and fueled wildfires. Park Williams, the lead author of the study just published in the journal Nature Climate Change, joins William Brangham with more. PBS NewsHour is supported by - https://www.pbs.org/newshour/about/funders