Rotkoff was also quick to note a major difference in their image: Julian Castro has served as mayor in a nonpartisan environment. Joaquin Castro, on the other hand, has been in the Texas Legislature during some of the more recent partisan state fights. One brother has built his image as someone able to govern, while the other is an effective political combatant.
"I think that obviously, the mayor has gotten an understandable amount of national attention, as he should as a fantastic mayor and future leader of the state, but I think it is a mistake to limit . that analysis with the mayor and not draw the same conclusions about Joaquin Castro," Rotkoff said.
Texas Republicans will concede that as the Texas Democratic Party struggles for relevance, either of the Castros are postured to be major political players when Hispanics are expected to heavily influence political demographics.
"In Texas in particular, there are only a handful of people you can look to as leaders in the Democratic Party and the Castros are people who are energizing to the base and are working to rebrand the party," a Texas Republican consultant said.
"I wouldn't discount one over the other," the consultant added.
Former Sen. Scott Brown, R-Mass., candidate for U.S. Senate in New Hampshire, holds his hand over his heart during the singing of the national anthem as he waits to take the stage for his town hall campaign rally with Sen. John McCain at the Pinkerton Academy in Derry, N.H., on Monday, Aug. 18, 2014.