What did Donald Trump do today?

He got told that he wasn't a king.

In both the impeachment inquiry and the Russia investigation, Trump has repeatedly ordered executive branch employees to refuse to appear before Congress—something he has no legal authority to do. This assertion of "absolute immunity" from any oversight whatsoever dovetails with Trump's claim, made last month in federal court, that he could even commit murder and be immune from any investigation at any level of government while he held office. 

Today, a federal judge issued an astonishingly long and detailed ruling making clear that neither Trump nor any other president has the power to simply ignore Congress's Constitutional powers of oversight.

The immediate effect is that Trump's former White House counsel, Don McGahn, will be required to appear before Congress. McGahn played a major role in the Russia scandal by refusing to allow Trump to further obstruct justice by firing the special counsel conducting the investigation, and other "crazy shit," to use McGahn's words. 

The ruling by federal district judge Ketanji Brown Jackson was unusually detailed and forceful. It stands a good chance of becoming binding precedent—because courts have never been forced to rule before on whether the presidency is somehow above all other branches of government. As Jackson put it in her summation:

Stated simply, the primary takeaway from the past 250 years of recorded American history is that Presidents are not kings. This means that they do not have subjects, bound by loyalty or blood, whose destiny they are entitled to control. Rather, in this land of liberty, it is indisputable that current and former employees of the White House work for the People of the United States, and that they take an oath to protect and defend the Constitution of the United States. Moreover, as citizens of the United States, current and former senior-level presidential aides have constitutional rights, including the right to free speech, and they retain these rights even after they have transitioned back into private life.

Trump is expected to appeal the ruling that he is not a king.

Why should I care about this? 

• It shouldn't take a federal judge to explain to a president that he is not above the law.