He spent several weeks trying to build his campaign around climate change, calling global warming the greatest existential threat the country had ever faced. But as the excitement over his candidacy began to fade, O’Rourke was forced to stage a “reintroduction” of his campaign to reinvigorate it. After a gunman opened fire at a Walmart in his hometown of El Paso, killing 22 people, O’Rourke more heavily embraced gun control, saying he would take assault weapons away from existing owners.