Republican-turned-Libertarian candidate Miguel Olivas announced on Facebook Monday that he will not run for Congress in Arizona's District 3.
A legal challenge to his nominating petitions found one signature was invalid, he said.
Remaining in the Republican primary race are Gabriela Saucedo Mercer, who won the party's nomination in 2012, and Mike Polak, who is running as a write-in candidate.
Besides Olivas, Damien Kennedy and Jaime Vasquez previously withdrew from the race.
Incumbent Democrat Raúl Grijalva is running for a seventh term in Congress. He won in 2012 with 58 percent of the votes.