The NTSB was formed by The Independent Safety Board Act of 1974. The NTSB was designed to be an independent agency not susceptible to the influence of other parts of government. The Board is managed by five "Members" appointed by the President, each for a five-year term. Once appointed, the member theoretically has job security for his full term, so if the White House calls, the Board theoretically doesn't have to jump. (They might only ask, "How high did you have in mind, Mr. President?")
This is a companion discussion topic for the original entry at https://www.avweb.com/aviation-news/ntsb-accident-investigations-what-you-need-to-know