The US strike on an oil tanker in the Gulf of Oman earlier this month did more than kill three Indian sailors and severely undercut US-India relations. It has also cast further doubt on the unity of the Quad, an informal bloc made up of the United States, Japan, Australia and India, and the group’s ambitious agenda aimed at loosening China’s dominant grip on critical minerals. Despite the persistent US-India fissures that could slow down the Quad’s momentum, however, a counter-unifying force may...