Even if the President has to have a good reason to do something, that has no practical effect on whether the President will do something. There will be no consequence to the President, and in most cases to his order followers, beyond "you shouldn't have done that" and much harumphing in Congress.

Social constructs are shared illusions that only work when we decide to adhere to them.

Hypothetically, Congress should have the authority to subpoena and then disclose classified information.

To my knowledge, it has not been tried.

Documents like this were requested during impeachment and were either not provided or heavily redacted in ways that suggest a cover up of damaging material not valid reasons allowed by law. The administration is already hiding critical information from the public because it might look bad for the president. This is the same thing but will directly impact our response and likely raise the fatality rate in the US.

Ah, okay. So Congress lacks that power because Congress decided it lacks that power.

It has, it just takes time. We're still waiting on the court decision about declassifying the Mueller report (the subpoena was just upheld at the appeals court level, we can assume that the Trump administration will appeal to the Supreme Court to try to keep the report secret).

In the spirit of the principle of charity, it isn't that hard to believe that part of the discussion is the impact the virus will have on classified activities, including but not limited to intelligence activities, military activities, or may have included information considered sensitive (like, just by way of example, proof that the virus was gene engineered, which may cause an undesirable international stink if publicized; I mention this just as an example of something that they might classify, not as a claim that it is engineered).

I'd expect "the President" did not literally decide or not decide to classify this; it was probably driven by rules.

What's in the classified briefings isn't really the question; it's what's in the unclassified briefings and actions that are the question. That classified briefings are taking place is to be expected, as it will certainly be impacting classified things, along with all the other "pretty much everything" it will be impacting. I'm sure all the other countries are having classified briefings as well.

“We had some very critical people who did not have security clearances who could not go,” one official said. “These should not be classified meetings. It was unnecessary.”

Said an official who may or may not have been in there; it wasn't clear from the article.

I assure you that these are hardly the only meetings taking place.

My question was more on legal authority than what actually happened in this particular case.

Does the President have the legal authority to just say "this thing is classified", and legally it is so?

In theory, it's only for things that can "cause harm to national security"

I suppose one could argue knowing or perceiving incompetence could lead to a national security issue.

Pretty sure that ship has sailed years ago.

Always worth noting when this topic comes up that the first time a classification was used to deny revelation of documents for "state secrets" reasons in a court of law, it turns out (we know this because the document has since been declassified as its classification expired) it was to shield the military from culpability in the death of civilian contractors in a plane that crashed due to a maintenance lapse.