The legal scholar Alan Dershowitz, just said on Fox News that President Trump could not have committed obstruction of justice because he was “simply exercising [his] power under the Constitution” when he fired Comey. This is not so.
It is true that the President has full authority to fire the FBI director. After all, the FBI Director and the Department of Justice are part of the Executive branch. The President has the duty to execute the laws. Therefore, the President can decide how and what laws should be executed in what way, as well as to appoint the people who will help exercise those duties (and fire the ones who will not). So, yes, as Mr. Dershowitz claimed, the President has the authority to fire the FBI director. There is a problem here, however. If Trump fired Comey to stop Flynn from being investigated, then Trump was not acting under the authority that the Constitution grants him. In other words, if all the allegations are true, the reason for firing Comey was not because Comey was hampering Trump’s ability to execute the laws. The reason for firing Comey was to corruptly help a friend avoid legal troubles. The Constitution does not grant this authority to the President.
Dershowitz’s statement is misleading because it ignores the motivation behind the firing. Even though the President has the authority to tell an FBI director, “don’t investigate this and focus on that,” the President cannot fire an FBI director in order to obstruct justice. The President can only fire the director if it’s related to his executive duties. But if he did it to “corruptly” impede Comey from investigating Flynn, then that – by definition – is obstruction of justice.