A former chief of staff to Sen. Ted Cruz announced he will run for the Republican nomination for Texas’ 21st District.

Chip Roy announced Wednesday he would seek the seat being vacated by GOP Rep. Lamar Smith, according to the Texas Tribune.

Smith announced last month he would retire following his final term as chairman of the House Science, Space and Technology Committee.

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Roy joins a crowded Republican field with more than a dozen candidates lined up for the district.

Among the Republican candidates are state Rep. Jason Isaac of Dripping Springs, former Rep. Francisco Canseco and former Bexar County Republican Party Chairman Robert Stovall.

Before working for Cruz, Roy worked for Attorney General Ken Paxton, former Gov. Rick Perry and Sen. John Cornyn.

The Tribune also reported that many Cruz alum are staffing Roy’s campaign, including Cruz’s 2012 senate campaign manager John Drogin; his chief presidential campaign strategist Jason Johnson and Jordan Berry, who worked on Cruz’s insurgent 2012 campaign.

Inside Elections with Nathan L. Gonzales rates the race Solid Republican.