Democratic presidential candidate, Sen. Bernie Sanders (D-VT), speaks at a campaign rally at Ventura College on May 26, 2016 in Ventura, Calif. (Photo by David McNew/Getty)

Sanders warns Clinton on running mate pick

Senator Bernie Sanders doubled down on his warning to Democratic rival Hillary Clinton that her pick for running mate will be critical to winning over his supporters going into the general election during an interview to air Sunday on "Meet the Press.