FILE - In a Friday, June 8, 2012, file photo, San Antonio Mayor Julian Castro gives the keynote address at the Texas Democratic Convention in Houston. Marking a first for Hispanics, the Democratic party announced Tuesday, July 31, 2012 that Castro has been chosen to deliver the keynote address at the Democratic National Convention on Sept. 4, 2012, the convention's opening night. (AP Photo/Pat Sullivan, File)

Photo by: Pat Sullivan

FILE - In a Friday, June 8, 2012, file photo, San Antonio Mayor Julian Castro gives the keynote address at the Texas Democratic Convention in Houston. Marking a first for Hispanics, the Democratic party announced Tuesday, July 31, 2012 that Castro has been chosen to deliver the keynote address at the Democratic National Convention on Sept. 4, 2012, the convention's opening night. (AP Photo/Pat Sullivan, File)