After months of speculation, U.S. Representative Joaquin Castro on Monday backed out of running for the U.S. Senate. Castro’s decision gives congressman Beto O’Rourke a clear path to the party nomination to challenge incumbent Ted Cruz in 2018. Castro, who represents San Antonio, cited both his family and his current U.S. House committee appointments as his reason for not running.

“Texans want a Senator who will stand up for their families, not stand down to Donald Trump,” Castro said in a statement. “I’ve kept my pledge to fight for hard-working Texans, and I’ll keep doing that. However, with the threats posed by Russia and North Korea, coupled with the reckless behavior of this Administration and their failure to invest in economic opportunity for the American people, at this time I believe I can best continue that work by focusing on my duties in the House Foreign Affairs and Intelligence Committees.”

O’Rourke represents El Paso, but he also had promised that he would serve only one more term in the House. He announced last month that instead of seeking a final House term, he would challenge Cruz. (Political strategist and television pundit Matthew Dowd is considering a possible independent run against Cruz.) Though a Texas Lyceum poll showed O’Rourke tied with Cruz, almost a third of those surveyed had no preference in the Senate race, and in recent years Republicans have had at least a 9-point advantage in Texas general elections.