Get your facts straight. Beto did not speak about gun control during his Senate campaign.
The year after he lost the Senate race to Cruz, Beto briefly campaigned for POTUS. It was during his presidential campaign that he brought up removing AR-15s and spoke about gun buyback programs.
Speaking about guns did not cost Beto the Texas Senate race because Beto is not a time traveler.
Beto didn’t say anything about guns until 2019, after he lost the Senate race, and then campaigned for POTUS.