The largest Border Patrol agents' union on Wednesday endorsed Sen. John McCain (R-Ariz), an important backing in what the 79-year-old senator said could be "the race of my life" against his Democratic challenger, Rep. Ann Kirkpatrick.

National Border Patrol Council (NBPC) President Brandon Judd said McCain has been instrumental in improving the working conditions of Border Patrol agents.

"Senator McCain understands the challenges we face out in the field," Judd said in a statement.

"Senator John McCain has led the fight in the U.S. Senate to provide the Border Patrol with resources to combat illicit activity and keep our communities safe,” NBPC Local 2455 President Art Del Cueto added.