Former President Donald Trump vowed to speak at this weekend’s National Rifle Association convention even after an 18-year-old gunman killed 21 people, including 19 children, at a Texas elementary school. Denouncing “politicians and partisanship,” Trump said he would appear as scheduled on Friday at the pro-gun group’s annual confab in Houston, about four hours east of the town of Uvalde where the slaughter unfolded. “Americans need real leadership and real solutions at this moment,” he wrote in a post on his new Truth Social platform. Trump echoed complaints by Republican leaders that Democra…