The group of agencies that works most closely with the president is

The executive office of the president made up of the OMB, the NSC, the Vice President, and the ONDCP.

These are the people, combined to form an agency, who work very closely with the president.

Explanation:
The Executive Office of the President of the United States is a group of agencies at the center of the executive branch of the United States federal government. It was created in 1939 by President Franklin D. Roosevelt to provide the President with the support needed to govern effectively.