Originally published in the New York Times By Katie Rogers INDIANAPOLIS — In a speech to National Rifle Association members on Friday that was part political rally and part pep talk, President Trump called himself a champion of gun rights. Then he proved it, whipping out a pen onstage to sign a letter that would effectively cease America’s involvement in an arms treaty designed to regulate the international sale of conventional weapons. Mr. Trump said that his administration “will never” ratify the Arms Trade Treaty, which seeks to discourage the sale of conventional weapons to countries that do not protect human rights. Although the accord was brokered by the United Nations and signed by President Barack Obama, it has never been ratified by the Senate. Experts in arms control note that the accord, even if ratified by the Senate, would not require the United States to alter any existing domestic laws or procedures governing how it sells conventional weapons overseas. S...