Question

As the president and the executive department implement and enforce a law. They might need

Answer 1

To implement and enforce a law, the president, and the executive department needs the senators and the representatives. 
The executives are responsible for the implementation and enforcement of laws headed by the President. But these laws are created by the legislative branch which is composed of the senate and the house of representatives.

Answer 2

As the president and the executive department implement and enforce a law. They might need "to interpret the details of a law".

The President is both the head of state and head of administration of the United States of America, and Commander-in-Chief of the military.

Under Article II of the Constitution, the President is in charge of the execution and implementation of the laws made by Congress. Fifteen official offices — each drove by a named individual from the President's Cabinet — complete the everyday organization of the government.