He may need new material. Mr. Castro, 38, is accustomed to being mistaken for his one-minute-older identical twin, Julián Castro, a rising political star who last summer became the first Latino to deliver a keynote address at the Democratic National Convention. In the two months since Mr. Castro, a lawyer and former state legislator, was sworn into Congress, he has been the twin receiving the larger share of attention. He received high-profile assignments to the Armed Services and Foreign Affairs committees and was elected president of the House Democrats’ freshman class. Although his own Congressional race was noncompetitive, he made fast friends and earned praise from the Democratic Congressional Campaign Committee for raising cash for future colleagues. And he has been an unofficial ambassador on immigration for the Obama administration, appearing on “This Week With George Stephanopoulos” on ABC the morning after the White House’s comprehensive immigration plan leaked. There he lauded the president’s efforts and highlighted what he called “commonalities” between the administration’s proposal and one by a bipartisan group of senators. “I’m trying to very quickly be as helpful as I can,” Mr. Castro said last week in an interview, “not only as a voice out there speaking about it in the news, but also internally, in the body.” Business Insider named Mr. Castro one of its “12 most fascinating new members” of Congress. And a study by the University of Minnesota Smart Politics project ranked him the second-most-talked-about House freshman in terms of news media coverage, edging out Steve Stockman, the Friendswood Republican who brought the Obama-bashing rocker Ted Nugent as a guest to the president’s State of the Union address. While there has been much public discussion about the ambitions of his brother to become governor, speculation is already mounting that Joaquin Castro could challenge Ted Cruz, the state’s Tea Party-backed junior United States senator, in 2018. “Certainly my brother being in the spotlight the way he was at the Democratic National Convention helped a lot in terms of exposing us to the nation,” Mr. Castro said. “That said, I think that you’ve got to do well when you have the opportunity or those opportunities will go away.” Mr. Castro has embraced the limelight and is leveraging the attention in many ways. He claimed one of the highly visible aisle seats hours ahead of the State of the Union address and uses distinctive wordplay to drive home one of his main messages, that education breeds prosperity for the underprivileged. In interviews and public appearances on a recent day in Washington, Mr. Castro used a term he coined — America’s “infrastructure of opportunity” — no fewer than six times. He has also become a serious student of domestic and international policy. The academic aspect is familiar territory for Mr. Castro, who with his brother attended Stanford University and Harvard Law School after being raised on the working-class west side of San Antonio by his mother, a political activist. He has surrounded himself with experienced staff members: his chief of staff is a former aide to Nancy Pelosi, the House minority leader, and his press secretary served Harry Reid, the Senate majority leader. In a 12-hour period last week, Mr. Castro jumped from a meeting on Islamic terrorists in Eurasia to a briefing on challenges to the Voting Rights Act and the Defense of Marriage Act. He gave his first one-minute speech on the House floor, on the effects of sequestration, approaching the dais minutes after Speaker John Boehner accused the president of playing politics. Afterward, Mr. Castro dashed across town to a forum on high school graduation and college readiness. Mr. Castro said it was too early to speculate on his political future. “A lot of folks feel like my brother and me or other politicians chart out their careers from Day 1 until the end. I’ve never been like that,” he said. “I just believe that if I work hard and do well, who knows what the future holds?” But he did not resist taking a thinly veiled jab at Mr. Cruz, who has made headlines in the Senate for a prosecutorial-style questioning of Mr. Obama’s defense secretary nominee, Chuck Hagel. “I didn’t come here to be a wallflower, but I didn’t come here to get into a shouting match with everybody I meet either,” Mr. Castro said. “Doing your job requires different modes, and you can’t just be stuck in one mode where you’re always the shrill outsider screaming at everybody.” The Castro brothers’ political allies credit them with boosting the national profile of Texas Democrats. State Representative Rafael Anchia, Democrat of Dallas, said they had “in a very short period of time almost single-handedly breathed life back into the Texas Democratic Party.” Ed Espinoza, an Austin-based Democratic consultant, said that among the rising Latino stars on both sides of the aisle, the Castros pose a big electoral threat. “I don’t think the G.O.P. has the answer for them,” Mr. Espinoza said. The state’s Republicans say they are unmoved. Jordan Berry, a political consultant who was on Mr. Cruz’s campaign, attributed the attention paid to the brothers to a “ ‘Parent Trap’ effect,” referring to the movie about identical twins, and said he was “confident in our bench over theirs” in the race to connect with the state’s rapidly expanding Latino population. Rob Johnson, a Republican operative who ran a “super PAC” in support of Mr. Cruz’s primary opponent, Lt. Gov. David Dewhurst, said party leaders were unworried. “We recognize that they’re talented politicians and political operatives, but this is also Texas, the reddest of the red states,” he said. “What we need to focus on is not what the other side is doing and saying, but what we as a party are doing and saying to grow our numbers among Latinos.” For his part, Mr. Anchia, the Democratic state representative, said he was happy to see Mr. Castro getting his due on the national stage. He said Mr. Castro had spent more time in the last few years working to get his brother elected mayor than on cultivating his own aspirations. “He sacrificed himself for his brother’s success,” Mr. Anchia said. “For someone who is equally bright, talented and ambitious, that was an admirable trait.” Mr. Castro said he was glad to play a supporting role and that he did not believe that he had lost out. “Somebody jokingly asked me a few years ago, ‘Who’s going to be the Jack Kennedy and who’s the Robert Kennedy?’ ” Mr. Castro recalled. “I said, ‘I’m glad to play the Robert Kennedy.’ ”
