What did Donald Trump do today?

He finally, once and for all, declared himself beyond any oversight or investigation.

Today, in a twelve-page letter to the chair of the House Judiciary Committee, White House Counsel Pat Cipollone laid out Trump's philosophy on Congressional oversight of the presidency: there isn't any.

In practice, this is a delaying tactic to keep materials that the House has subpoenaed under wraps for as long as possible. The right of Congress to conduct oversight, by subpoenaing evidence and hearing testimony from White House staff, has been settled law since 1880 at the latest. 

But in principle, at least, Trump is simply saying that Congress can't act as a check and balance against the presidency when he doesn't want it to. By this standard, Congress would not have been able to investigate Watergate, the Iran-Contra affair, the response to Hurricane Katrina, waste and fraud in wartime contracting, the infiltration of civil rights groups by the FBI, what the intelligence community knew or should have known about the September 11th attacks, how federal law enforcement deals with domestic terrorists, or really any other matter involving the presidency in any way. It also would have been powerless to conduct the investigations that led to the impeachment of Presidents Johnson or Clinton, or any executive branch official.

In addition to saying that Congress cannot subpoena executive branch records, Trump has also declared that as president, he cannot obstruct justice, cannot corruptly exercise their powers, cannot be indicted, cannot be forced to release his tax returns to Congress, can stop any investigation into crimes he feels himself to be "falsely accused" of, and cannot be impeached (as long as he feels he's "doing a great job"). 

He's also insisted that he has the authority to pardon himself for the crimes he says he cannot be investigated, indicted, or impeached for.

Why should I care about this?

• Presidents are not kings or dictators.

• The Constitution of the United States is the supreme law of the land, even when it's politically inconvenient for the president.