In his opening weeks back in office, President Trump is asserting power in a way that pushes hard on, and sometimes past, the boundaries of executive authority.

One of the most important of those boundaries involves his relationship with independent regulatory agencies. Mr. Trump is the first president since the 1930s to assert control over many of them, and this assertion of power will almost certainly be tested in the Supreme Court.

Mr. Trump is operating under the theory that the executive branch is unitary, in the sense that Article II of the Constitution places executive power in a single person, the president, who gets to control every high-level official who executes federal law (and plenty of lower-level ones, too).

If Mr. Trump succeeds in court, the country will see a significant shift in power from the independent agencies to the White House.

For better or for worse, that shift would be profoundly unsettling. And in some respects it could be dangerous — if, for example, a president is allowed to control monetary policy, or if he is in charge of the Federal Communications Commission, and thus able to play politics with national communications policy.

The president is not a king. In its most extreme version, the unitary executive theory is a form of invented history, a modern creation that threatens to change, and in important ways to undermine, the operations of the national government.