By unsheathing the oil weapon, the Saudis have finally tested the patience of oil-patch Republicans, who have long been among their staunchest supporters in Congress. Even though the United States, Saudi Arabia, Russia, and other big oil producers reached a deal this month meant to curtail oil output and undo some of the damage, it hasn’t worked: U.S. crude oil prices are at their lowest levels of the 21st century, threatening mass bankruptcies and layoffs in the United States.