As the United Nations General Assembly gathers in New York City this week, the war in Gaza and the issue of Palestinian statehood will dominate much of the debate. But notably absent will be the Palestinian leaders themselves. Because the United Nations headquarters is in New York City, the United States is the country that issues visas to the leaders and diplomats who travel to the event. The State Department said that the decision to deny Mr. Abbas a visa was made on grounds of national security. The United States says Palestinian statehood must be negotiated between Israel and the Palestinians.