PHILADELPHIA — When it came time for the roll call vote here at the Democratic National Convention, Texas Democrats were ready to share some history. 

Announcing the state's votes for Hillary Clinton, state party Chairman Gilberto Hinojosa hailed the Lone Star State as "home of Democratic giants like Lyndon Baines Johnson, Barbara Jordan, Ann Richards and the twins Joaquin and Julián Castro." 

While those last two names don't yet carry the weight of the first three, their inclusion underscored just how much hope a state Democratic party seeking a path out of political exile is placing on the Castro brothers. The party's next big opportunity comes in 2018, when the state's top elected officials — all Republican — are up for re-election. That includes perhaps the biggest prize, the U.S. Senate seat held by Ted Cruz

The festivities here put on display the early jockeying for those races, with much attention focused on San Antonio Congressman Joaquin Castro — who catapulted into headlines after saying in a TV interview Tuesday that he will consider challenging Cruz.

The Texas Tribune thanks its sponsors. Become one.

Other potential candidates are holding their cards closer to their vests, well aware that their chances in 2018 could depend on the outcome of the presidential race between Clinton and Donald Trump. 

Trump "would be an unmitigated disaster as president," former Houston Mayor Annise Parker said. "Temperamentally, he is unfit to be president of the United States, and there is no doubt that after he creates the train wreck, it would be a good thing for Democrats. It would not be a good thing for our country. So we're going to stop him."

As for herself, Parker said she is "looking at statewide races" but may be more inclined to run for office in Harris County in 2018. "I'm keeping an open mind," she added.

Parker was among six "Texas stars" the state party identified to reporters ahead of the convention, a list that also included Dallas County Sheriff Lupe Valdez, Austin Mayor Steve Adler, Travis County Democratic Party Chairman Vincent Harding, state Rep. Helen Giddings of DeSoto and Clarissa Rodriguez, a 17-year-old from Texas City who was the youngest delegate in Philadelphia. Valdez ended up with a speaking slot on the last night of the convention, leading a tribute to law enforcement and pleading with Americans to "start listening to each other." 

Ask some Texas Democrats about 2018, though, and few names come up besides the Castro brothers. "I'm saying Joaquin because he has that national presence and he's already put some feelers out that he may run," said state Rep. Carol Alvarado of Houston, insisting she did not want to "zero in just yet" on Democrats who could run in two years.

Former Land Commissioner Garry Mauro said he cannot imagine Democrats not running statewide in 2018. But asked to name names, he declined. 

The Texas Tribune thanks its sponsors. Become one.

"When we have a visionary leader, we'll win," said Mauro, a longtime Clinton ally in Texas. "Whether we like it or not, the reason the Republicans took over was because they had somebody they considered a visionary leader beat Ann Richards — George W. Bush."

Other state Democrats point to the state's biggest population centers as natural breeding grounds for up-and-comers. Four of the state's top five largest cities are effectively led by Democrats, though some may consider San Antonio's Mayor Ivy Taylor, a registered Democrat, more of an independent.

"What you’re seeing in a Texas is that all the larger, more urban areas are beginning to be controlled by Democrats and the leadership in those areas naturally are the mayors and county judges," Hinojosa said in an interview on the eve of the convention. Such officials, he added, "have those credentials to eventually rise up and take a leadership role" at a higher level. 

That was reflected in the lineup for the state delegation breakfast Wednesday, which featured Parker, Adler and Houston Mayor Sylvester Turner. Texas delegates also heard that morning from Los Angeles Mayor Eric Garcetti, who expressed hope that "Donald Trump in Texas is like what Pete Wilson was in California." (Wilson, the former GOP governor of Golden State, pushed restrictive immigration policies in the 1990s that some credit with help turn the state blue.)

"Our Democrat-led cities are thriving," Hinojosa told delegates that morning.

In any case, most conversations about the future of the Texas Democratic Party lead back to the Castros, by far the most in-demand Texas Democrats in Philadelphia. Julián Castro, the U.S. housing secretary, was dealt some disappointment three days before the convention, when Clinton passed him over for running mate, instead picking U.S. Sen. Tim Kaine of Virginia.

"Who knows what's next?" Julián Castro told The Texas Tribune on the opening night of the convention. He did seem to rule out one future job: chairman of the Democratic National Committee, after Debbie Wasserman Schultz stepped down at the end of the convention following a scandal over leaked DNC emails that threw into question the committee's neutrality in the presidential nominating process. 

Joaquin Castro, the San Antonio congressman, appeared more willing to stoke speculation about his political future. After the TV interview — in which he said he is "going to take a look" at challenging Cruz — he spent the next two days needling Cruz, painting him as a self-interested politician increasingly out of step with Texans and dinging him during his speech on the final night of the convention. 

The Texas Tribune thanks its sponsors. Become one.

Of all the speakers who paraded before Texas delegates at their daily convention breakfasts, Castro offered perhaps the most clear-eyed take on the future of the state party, warning Texas Democrats against waiting around for voters to grow fed up with an increasingly conservative state government. 

"Everybody gets this question around here, especially because you're around people from other states. 'When is Texas going to be competitive?' 'Is Texas going to turn blue?'" Castro said. "Listen, y'all, the answer is that we are competing against ourselves. It depends upon us and what we do. Our fate does not lie in the hands of Republicans who keep going further and further to the right."

"Every time they do something that crosses the people of Texas," Castro added, "we need to call them out for it and we can't be shy about it."

Whatever path Texas Democrats chart forward, their Republican counterparts appear ready to aggressively beat back any challenges, and paint them as an assault on the state's modern GOP tradition. That was the theme of two fundraising emails Cruz and his political team sent out this week, first in reaction to Castro's flirtation with a challenge then in response to an interview in which Wendy Davis, the former Democratic gubernatorial candidate, did not rule out her own run against Cruz. 

The latest Texas Republican to get in on the action was Gov. Greg Abbott, whose political shop on Friday blasted out a Philadelphia-themed email to supporters asking for money. 

"There have been plenty of rumors during the Democrat convention about who will try to defeat Governor Abbott in 2018," wrote John Jackson, Abbott's campaign director. "The Castro brothers and Wendy Davis don’t deny that they’re keeping their options open. "

In an interview Wednesday with the Tribune, Davis specifically said she was not considering a challenge to Cruz. But she suggested Texas Democrats should not shy away from uphill battles — much like her race against Abbott in 2014, when he beat her in a landslide despite intense national interest in her candidacy. 

"It’s tough," Davis said when asked about the Democratic bench in Texas. "I think it’s one of the reasons that we need to do these hard races. It’s not just about the win. It’s about building the voter file. It’s about building the talent pool."