You cannot be ordered to violate the Constitution. Stopping an investigation into government corruption because the very people who might be involved is a violation of the Constitution. Anyone giving that order is giving an unlawful order, period.
If you do not understand the law or the Constitution, you are not fit to be in office, nor in government service of any type. Ignorance is no excuse, nor a viable defense, for government servants.
The FBI Agents who obeyed should be prosecuted, as well. They are bound to the Constitution, not to elected, un-elected, or employed bureaucrats.
You cannot be ordered to violate the Constitution. Stopping an investigation into government corruption because the very people who might be involved is a violation of the Constitution. Anyone giving that order is giving an unlawful order, period.
If you do not understand the law or the Constitution, you are not fit to be in office, nor in government service of any type. Ignorance is no excuse, nor a viable defense, for government servants.