Federal obstruction of justice statutes bar anyone from interfering with law enforcement, including official investigations, based on a “corrupt” motive. But what about the president of the United States?
The president is vested with “executive power,” which includes the power to control federal law enforcement. A possible view is that the statutes do not apply to the president because if they did they would violate the president’s constitutional power. However, we argue that the obstruction of justice statutes are best interpreted to apply to the president, and that the president obstructs justice when his motive for intervening in an investigation is to further personal or narrowly partisan interests, rather than to advance the public good.Daniel Jacob Hemel and Eric A. Posner, "Presidential Obstruction of Justice" SSRN (July 18, 2017) (emphasis and paragraph break added).
Another concept that really ought to enter constitutional law is that the executive branch is not unitary (something also well established in French political theory that conceptualizes the civil service as one of the major branches of government).
There are independent agencies designed by Congress with the consent of the Presidency that are insulated, by design, from the direct control of the President. There is also a division between the political leadership made up of Plum Book officials and the civil service that is made up of employees and contractors selected on a merit system who can only be removed from office for cause or via impeachment. And, there are ethical obligations owed by all public officials, to the entity, the United States government and the United States Constitution, and not to the individual, the currently incumbent President of the United States.
Once the executive branch of the United States government is disaggregated in this fashion, the notion that a President can obstruct justice by taking efforts to interfere with the criminal justice functions of the civil service, not as a matter of policy, but for personal or partisan gain, becomes much more clear and free of paradoxes.