Trump is not their employer. American citizens are. We pay their salaries. Their oath is to the constitution, not Trump.
Their job is to support their agency’s mission relative to the program they are working on. Congress funds these agency/programs with a particular purpose in mind. It is not the job of a president to direct personnel to subvert the purpose of the program Congress has authorized with his own personal agenda which is what Trump has often tried to do.
From the White House website, note that Congress writes the laws, the Executive branch carries them out:
“The power of the Executive Branch is vested in the President of the United States, who also acts as head of state and Commander-in-Chief of the armed forces. The President is responsible for implementing and enforcing the laws written by Congress and, to that end, appoints the heads of the federal agencies, including the Cabinet. The Vice President is also part of the Executive Branch, ready to assume the Presidency should the need arise.
The Cabinet and independent federal agencies are responsible for the day-to-day enforcement and administration of federal laws.”
From the President, to the Vice President, to the Cabinet, learn more about the Executive Branch of the government of the United States.
www.whitehouse.gov