He dismisses the Obama comparisons and claims that he will serve as mayor until 2017, when he is term limited. After that, Castro said he will consider his options. He doesn't outright say he doesn't want to run for president one day, but he calls the prospect unlikely.
"It's very likely that the first Latino president has been born, [but] I don't think that I'm going to be that person," he said. Castro says he has a tough path upward in Texas. There are 29 statewide elected offices in the Lone Star State and a Democrat has not held one since 1994.
Asked if he would turn down a potential cabinet appointment, to a position such as Secretary of Housing and Urban Development, the position his role model Cisneros held in the Clinton administration, Castro says he would.
"Yeah," he said. "I can't imagine what they would offer me."
Castro says he is trying to stay focused on giving a memorable speech on Tuesday, not on what might lie ahead.
"I would be lying if I said I wasn't a little bit nervous because it's such a huge opportunity. But I'm also taking it very seriously and I know it's a great chance to speak to the nation in a meaningful way," he said. "So I'll be ready by the time I take the stage. My boots might be shaking, but I'll be ready."
This piece is based on interviews conducted by Univision's Maria Elena Salinas as well as the author.