HOUSTON — Former President Donald Trump is defending the rights of gun owners in remarks to the National Rifle Association’s annual convention in Houston, three days after a gunman killed 19 students and two teachers at an elementary school on the other side of the state. With protesters shouting outside, Trump was set to call Friday for “drastically” changing the nation’s approach to mental health” and “a top-to-bottom security overhaul at schools across this country,” while dismissing calls to disarm gun owners, according to excerpts of his speech. “The existence of evil in our world is not a reason to disarm law-abiding citizens — the existence of evil is one of the very best reasons to arm law-abiding citizens,” he says in prepared remarks. Trump was among the Republican leaders lining up to speak at the event, where the gun rights lobbying group said attendees planned to “reflect on” — and deflect any blame for — the school shooting in Uvalde.