At a time when the Trump administration’s robust defense of Israel at the United Nations is shaking up an institution that has long been hostile to the Jewish state, the biggest bloc of developing nations at the U.N. has decided to bestow its presidency on the “State of Palestine.” The move looks likely to increase pressure on the U.S. and Israel in the U.N. General Assembly, where the U.S. already invariably loses Israel-related votes by heavily lopsided margins. There is no sovereign state of Palestine, but the self-rule Palestinian Authority chaired by Mahmoud Abbas has since 2012 enjoyed the status...