After delivering the keynote address at the Democratic National Convention on Tuesday night, San Antonio Mayor Julian Castro appeared to be living up to the tradition of keynoters from years gone by in at least one respect: He generated significant buzz about his future.

Castro’s address included some sharp critiques of Mitt Romney’s economic policies and drew on his own compelling personal story — which, like that of keynote speaker Barack Obama in 2004, includes inspiring anecdotes of family sacrifice. In Castro’s case, part of the tale is his grandmother’s immigration from Mexico, which he portrayed as an all-American story.

“My family’s story isn’t special,” Castro said. “What’s special is the America that makes our story possible.”

In criticizing Romney, Castro depicted the Republican presidential nominee as perhaps a decent person — but deeply out of touch. “Mitt Romney, quite simply, doesn’t get it,” Castro said. “A few months ago, he visited a university in Ohio and gave the students there a little entrepreneurial advice. ‘Start a business,’ he said. But how? ‘Borrow money if you have to from your parents,’ he told them. Gee, why didn’t I think of that? Some people are lucky enough to borrow money from their parents, but that shouldn’t determine whether you can pursue your dreams. I don’t think Governor Romney meant any harm. I think he’s a good guy. He just has no idea how good he’s had it.”

By Wednesday, the Obama comparisons were firmly in hand, and Castro was making the rounds of cable shows and political panels in Charlotte. Everywhere he went, the question persisted: Where will his career go next?

As the fast rise of Sen. Marco Rubio (R-Fla.) has shown, there is plenty of appetite in both parties for promoting young, smart and attractive Latino candidates.

But Castro — along with identical twin brother and fellow rising star Joaquin Castro — faces an obstacle: his home state.

Although Julian Castro is mayor of one of the largest cities in the country and Joaquin Castro, a state legislator, is heavily favored to win a congressional seat in November, there would be challenges for either of them in making the leap to statewide office.

Texas has not elected a Democratic governor or senator since Ann Richards won the gubernatorial race in 1990. The last Democrats elected statewide in Texas were lieutenant governor and attorney general, in 1994.

“Were he to run statewide at this point, he would have more potential than any Democratic statewide candidate fielded in the last decade,” Jim Henson, a pollster and political science professor at the University of Texas, said of Julian Castro. “But whether the votes are actually there in a state where election turnout is still dominated by Republicans — and very conservative Republicans at that — is still a very difficult [question] for even a strong Democratic candidate like Castro.”

At the same time, things are changing in Texas, with the Latino population accounting for two-thirds of the state’s huge growth over the past decade. The state no longer features a white majority, and if the Latino population continues to grow as quickly as it is now and continues to lean heavily Democratic, Texas could morph from firmly Republican to mixed.

Julian Castro said Wednesday that it could happen sooner than most people realize. “Those trends are going to cause the state to go purple and then blue within the next six to eight years,” he said.

By 2020, the state could feature more Latino residents than whites, and whites could be less than two-fifths of the population. Whites will probably still vote in higher numbers, given that many Latinos are young or not registered to vote. But there is potential for a shift.

Currently, Democrats can generally win about 45 percent of the vote in Texas, but they struggle to get beyond that. Democrats say a big part of that struggle has been their lack of strong potential recruits — a problem that the Castros would seem to help solve.

“Julian now can call upon and meet with Democratic donors and leaders in other parts of the country who would have otherwise not taken the time to get to know him,” said Texas Democratic consultant Matt Angle. “He is a fresh face, his story is compelling, his leadership qualities are apparent.”

Castro, meanwhile, is being coy, saying he’s happy in his role as mayor of San Antonio.

But he said it’s only a matter of time for his party in Texas.

“The day is coming when Texas will do that,” Castro said, referring to Democrats winning statewide office in Texas. “I don’t know if that’s the case yet, but it’s getting closer and closer.”

Ed O’Keefe contributed to this report.