President Trump vowed to crack down on undocumented immigration and empower the Border Patrol. Three years later, the agency is the target of outrage, protest and investigation into its mission and conduct, and many of the agents who have supported Mr. Trump say that morale is low. We spoke with one of them. Guest: Art Del Cueto, a Border Patrol agent in Arizona and vice president of the National Border Patrol Council. For more information on today’s episode, visit nytimes.com/thedaily.  Background reading: Overwhelmed by desperate migrants and criticized for mistreating those in their care, many agents, whose work has long been viewed as a ticket to the middle class, have grown frustrated and bitter.