Personal opinions aside, the president has authority to run the Exectutive branch of government as they wish. We have checks and balances in place to prevent overreach though if the White House is to be investigated it should be done through the legislative or judicial branches of government. If investigations are occurring within the FBI and going in a direction the president does not like then they have every right to change the director. This is why we have investigative committees that may be formed in congress. In the case of investigations of executive government entities, the president would have no power to remove those who head or comprise such a team.