In a move that crosses a threshold rarely breached in decades of Persian Gulf brinkmanship, the United States military has struck three Iranian crude oil carriers, according to a Saturday announcement from Central Command. The targeting of commercial petroleum vessels — the economic arteries of the Iranian state — marks a departure from the proxy skirmishes and naval posturing that have long defined this rivalry. Whether this represents a calculated act of deterrence or the opening of a new and more dangerous chapter will depend, in no small part, on how Tehran chooses to answer.