Philippine President Rodrigo Duterte this week announced the termination of a security pact that underpins the U.S.-Philippines alliance, and President Trump responded by celebrating potential savings for the American fisc. The good news is that this isn’t a popular decision in Manila or Washington, and there’s time to save the agreement.

The 1998 Visiting Forces Agreement facilitates the movement of U.S. troops and equipment into the Southeast Asian nation. This makes it possible for the countries to cooperate against terror...