Once the policy is developed to address an issue who implements and enforces it

The answer is:

A policy is implemented and enforced by all three the legislative, judicial and executive branches of government.

Explanation:

The legislative branch, made up of both the House and Senate implement the legislative process and no legislation can be enacted without the consent of both chambers.

The judicial branch rules on all matters related to the law of the constitution.

And finally the Executive branch enforces laws.