Since the start of Israel’s war in Gaza nearly two months ago, outraged young Americans have been at the forefront of a growing Palestinian solidarity movement. They have led protests in Washington and across the country to demand a permanent ceasefire and to voice their disapproval of Joe Biden’s support for Israel’s military campaign, which has killed thousands of Palestinians, mostly women and children, and plunged Gaza into a humanitarian catastrophe. A generational divide on the conflict is shifting the terms of the foreign policy debate in Washington, where support for Israel has long been bipartisan and near-unanimous. And, ahead...