After Watergate, it was unthinkable that a president would fire an F.B.I. director who was investigating him or his associates. Or force out an attorney general for failing to protect him from an investigation. Or dangle pardons before potential witnesses against him.

But the end of the inquiry by the special counsel, Robert S. Mueller III, made clear that President Trump had successfully thrown out the unwritten rules that had bound other chief executives in the 45 years since President Richard M. Nixon resigned under fire, effectively expanding presidential power in a dramatic way.

Mr. Mueller’s decision to not take a position on whether Mr. Trump’s many norm-shattering interventions in the law enforcement system constituted obstruction of justice means that future occupants of the White House will feel entitled to take similar actions. More than perhaps any other outcome of the Mueller investigation, this may become its most enduring legacy.

To Mr. Trump and his allies, this is the correct result, a restoration of the rightful authority of a president over the executive branch as stipulated in the Constitution. Under the theory that Mr. Trump’s legal team advanced, the Justice Department and the F.B.I. work for the president and therefore a president can order investigations opened or closed, fire prosecutors, grant pardons or otherwise use his constitutional power even if it seems overtly self-interested or political.