House Republicans are demanding to know how a gunman was able to wound former President Donald Trump during a deadly sniper attack at a campaign rally in Pennsylvania. Oversight Committee chairperson James Comer called for a Secret Service briefing on the incident, he said in a statement posted on the committee’s website. The Kentucky Republican also invited Secret Service Director Kimberly Cheatle to voluntarily appear at a July 22 hearing. “There are many questions and Americans demand answers,” Comer said. Rep. Mark Green, who chairs the Homeland Security Committee, said in a Sunday letter …