Obama's state director for Texas, Adrian Saenz, said the campaign understood the bar was high because of the Clintons' history and popularity. He said Obama, an Illinois senator who would be the first black U.S. president if elected, had spread his resources throughout the state to counter Clinton's strength, especially among Hispanics.

"The notion was that Senator Clinton was really strong in south Texas and that was Clinton country down there," he said. "She was down there this week and drew a crowd. We were down there a couple days later and drew a crowd that was almost twice as big."