When Ben Masters began the 1,200-mile journey along the Rio Grande to film his new documentary “The River and the Wall,” he had no idea the border wall would dominate politics the way it does today. Nor did he think, as he spoke with such locals as Beto O’Rourke and Will Hurd, that their voices would resonate so far beyond the border. Now the movie, making festival rounds and set for a May 3 release, profiles the debate deftly and shows off the unparalleled beauty of the region as Masters and four friends traverse the border on bike, foot, horseback and canoe. It’s funny, resonant, breathtaking and also a good old fashioned road movie. Masters discussed it after the film was the opening night attraction at this year’s Environmental Film Festival in the Nation’s Capital on the latest Political Theater podcast.