WASHINGTON — The Trump administration declared on Monday that the United States does not consider Israeli settlements in the West Bank a violation of international law, reversing four decades of American policy and removing what has been an important barrier to annexation of Palestinian territory. The announcement by Secretary of State Mike Pompeo was the latest political gift from the Trump administration to Prime Minister Benjamin Netanyahu, who has vowed in two elections this year to push for the annexation of the West Bank. His chief opponent, Benny Gantz, has until Wednesday night to gather a majority in Israel’s Parliament or he will relinquish his chance to form a new government, raising the prospect of a third round of elections.