The president believes he is above the law. That’s the takeaway from the confidential 20-page memo sent by President Trump’s lawyers to the special counsel, Robert Mueller, published over the weekend by The Times. And it’s the same sentiment that Rudy Giuliani expressed on Sunday when he suggested that Mr. Trump has the power to pardon himself.

The central claim of the legal memorandum is that it is impossible for the president to illegally obstruct any aspect of the investigation into Russia’s election meddling. That’s because, as president, Mr. Trump has the constitutional power to terminate the inquiry or pardon his way out of it. Therefore — and this is the key and indefensible point — he cannot obstruct justice by exercising this authority “no matter his motivation.”

This understanding of presidential power is radical and absolutist. It is also unsound and almost certain to be sharply rejected should it ever be proffered in court.

Even granting the contention that Mr. Trump could simply terminate the investigation, it is a non sequitur to argue, as the president’s lawyers do, that as a consequence he cannot obstruct it. Imagine, for example, that the worst version of facts proves true: that Trump fired the F.B.I. director, James Comey, tried to fire Mr. Mueller, constructed a false account of the June 2016 Russia meeting, and tried to force Attorney General Jeff Sessions to reverse his recusal decision that was driven by Justice Department policy, all to protect his own skin and his family’s fortune.