Question

When was a state obligated to follow the Constitution

Answer 1

A state was obligated to follow the constitution when they signed it and also decided to join the U.S. as a state
Hope this helps

Answer 2

after a majority of states had ratified it

Explanation: If a state was outvoted, they had to accept the new rules. BUT, they could still ask for favors in return. For example, New York and Virginia asked for favors when they were outvoted for the Federalist vs Anti-Federalist argument.