Rep. Joaquin Castro, D-Texas, accompanied by other member of Congress, speaks about a resolution to block President Donald Trump's emergency border security declaration on Capitol Hill, Monday, Feb. 25, 2019 in Washington. House Democrats have introduced a resolution to block the national emergency declaration that President Donald Trump issued last week to fund his long-sought wall along the U.S-Mexico border, setting up a fight that could result in Trump's first-ever veto. (AP Photo/Alex Brandon)

Rep. Joaquin Castro, D-Texas, accompanied by other member of Congress, speaks about a resolution to block President Donald Trump's emergency border security declaration on Capitol Hill, Monday, Feb. 25, 2019 in Washington. House Democrats have introduced a resolution to block the national emergency declaration that President Donald Trump issued last week to fund his long-sought wall along the U.S-Mexico border, setting up a fight that could result in Trump's first-ever veto. (AP Photo/Alex Brandon)

AUSTIN, Texas (AP) — Democratic Rep. Joaquin Castro of Texas confirmed Friday that he will “seriously consider” running for U.S. Senate against Republican incumbent John Cornyn, raising the remarkable possibility of charging into one of 2020′s biggest races at the same time his twin brother is running for president.

Julian Castro, the former Obama Cabinet member and San Antonio mayor, was among the first this year to launch a presidential campaign in what is becoming an increasingly crowded field of Democratic hopefuls.

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His run for the White House disappointed some Democrats who wanted him to stay in Texas, where Beto O’Rourke’s narrow loss against Republican Sen. Ted Cruz showed that a generation of GOP dominance in the state is suddenly fragile. But now Joaquin Castro, who passed on challenging Cruz in 2018, is thinking about picking up where O’Rourke left off.

“Congressman Castro will seriously consider running for Senate in 2020,” campaign adviser Matthew Jones said in a statement. “Right now, he’s focused on protecting Texans - and all Americans - from the most consequential challenge to our constitutional separation of powers that we have seen in a generation.”

The statement did not indicate when Castro would make a decision, but at the moment, Cornyn has no clear rivals.

O’Rourke has signaled he’s not in the Senate mix as he promises to announce soon whether he will run for president in 2020. On Friday, Washington Gov. Jay Inslee became the latest Democrat to jump into the presidential race, but O’Rourke and former Vice President Joe Biden remain the biggest potential contenders still on the sidelines.

Cornyn, 67, has been in the Senate since 2003 and is among its most powerful figures. He had been the No. 2 Republican in the chamber before being term-limited out of that leadership role this year and has never faced a serious re-election challenge.

But O’Rourke, who came within three points of Cruz in 2018, changed overnight what Democrats thought was possible in Texas, where they haven’t won a statewide office in 25 years. At the same time, Cornyn is a different incumbent from Cruz, who was widely derided by leadership of both parties for insurgent, trouble-making ways in the Senate.

Joaquin Castro, 44, is chairman of his brother’s presidential campaign. But his own profile is also rising in Congress, where he is chairman of the Hispanic Caucus and sponsored a measure passed Tuesday that would stymie President Donald Trump’s bid for billions of extra dollars for a U.S.-Mexico border wall.

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The Castros started their political careers around similar times but took different paths. Joaquin Castro made a slow climb to Congress after a decade in the state legislature, while Julian Castro quickly became one of Democrats’ most prominent Hispanic up-and-comers after being elected San Antonio mayor at age 34.

“I think he’d beat him. My brother would win,” Julian Castro told The Associated Press during a campaign stop in Nevada on Thursday. “There are a lot of Texans that clearly have problems with the way that he has represented the state. Most recently, refusing to stand up to Trump even though a lot of land is going to get taken, a lot of Texas landowners’ property is going to get taken if there’s a wall.”

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Follow Paul J. Weber on Twitter: www.twitter.com/pauljweber