Mr. Mansour detoured from diplomatic life starting in 1994, joining the management of an Orlando investment firm and teaching at the University of Central Florida, among other pursuits. He returned to the United Nations in 2005 as ambassador of the Palestinian observer mission, which was not then regarded by the global body as representing a state.

He is perhaps best known for tactics advancing the cause of Palestinian statehood in ways that have bypassed Israel. Seven years after his return to the United Nations, the body recognized Palestine as a nonmember observer state, an upgrade that gave the Palestinians the right to join global treaties and groups including the International Criminal Court, and one that angered Israeli officials and their American allies.

In Mr. Mansour’s view, such tactics are necessary because direct talks between Israel and the Palestinians have done little and, he says, Mr. Trump has corrupted the United States as a mediator.

Breaking with decades of American policy, Mr. Trump relocated the United States Embassy last year from Tel Aviv to the holy city of Jerusalem — which the Palestinians also want as their future capital. This year Mr. Trump terminated American funding to the United Nations agency that helps the roughly five million Palestinians who are registered as refugees.

This month, the American ambassador to Israel, David M. Friedman, suggested in an interview with The New York Times that Israel could annex parts of the West Bank, where Israeli settlements are regarded by much of the world as illegal.

Such steps, Mr. Mansour said, all point to what he called an unacceptable outcome from Mr. Kushner’s long-awaited peace plan.