Rep. Joaquin Castro says he will not run to challenge Sen. John Cornyn in Texas

U.S. Rep. Joaquín Castro said Wednesday that he will not enter the race to challenge U.S. Sen. John Cornyn, R-Texas, for his seat in 2020. The Democratic congressman from San Antonio had said in early March that he was considering a run.

“Right now, I’m going to focus on my work in the House of Representatives. I’ve been doing what I feel is important and meaningful work here,” Castro told the San Antonio Express-News.

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Rep. Joaquin Castro suggested he might run in March. 

Rep. Joaquin Castro suggested he might run in March.  (Fox News )

U.S. Air Force veteran Mary Jennings “MJ” Hegar, who served in Afghanistan, is currently the only Democrat running against Cornyn, but other candidates could enter the race, Politico reported.

Joaquin Castro is the twin brother of Julián Castro, a former San Antonio mayor and member of former President Barack Obama's Cabinet who is running for president.

Joaquin Castro’s decision to not enter the Senate race could help Democrats avoid a drawn-out and expensive primary process that could cost them the seat, Politico reported.

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Castro has served in Texas's 20th Congressional District since 2013.