WASHINGTON — The United States under the Biden and Trump administrations has provided at least $21.7 billion in military assistance to Israel since the start of the Gaza war two years ago, according to a new academic study published Tuesday, the second anniversary of the Oct. 7, 2023, Hamas attacks in Israel that provoked the conflict . Another study, also published by the Costs of War project at Brown University’s Watson School of International and Public Affairs, says the U.S. has spent