I cannot envision any terrorist attack that poses an existential threat to the United States. Fighting terrorism is not a national security matter. Even the largest terrorist attack in the history of the world (not counting the atomic bombings of Japan, which were terroristic by definition but generally excluded from that classification as being carried out during a declared war by a with-a-return-address nation) was
at least an order of magnitude off from posing a threat to the national security of the US.
"National security" is one of those thought-ending phrases that's thrown about to make people stop thinking critically about the matter. Terrorism is extremely bad, but it's not an existential risk, by its very definition.
> let’s acknowledge that there is at least a plausible national security reason for the US government to request things from Twitter
There is already a system that permits the government, investigating crimes, to compel information disclosure from a provider. It's called a search warrant, and requires a (very cursory, heh) review by a judge.
The government is asking not only for the power to skip that step (they've already taken that - that ship has sailed), but to prevent people from disclosing just how many times that's happened.
"National security" is not an umbrella term that means "bad things happening to USians", although I'm sure that the people using it in this instance as a cover story for widespread, illegal, extrajudicial espionage activity by the government would prefer that you think of it that way.
Remember: every legitimate NSL could have been a warrant. There's already a legal framework for how to investigate and prevent crimes, including mass murder. Additionally, anyone who's ever read a US federal warrant for anything involving sequences of bytes or information technology of any kind knows that the burden is already hilariously bad/low, and that they're very close to being rubber-stamp already. I personally have never seen a federal warrant (they're written under penalty of perjury) that didn't have naked factual errors in it, and I've only seen the ones that got approved/signed by a judge. There's a 100%, easily falsifiable, perjury rate in them in my experience. AFAIK none of the federal agents who have signed these sworn statements have ever faced any negative repercussions whatsoever for the falsehoods contained therein.
So, that hilariously low/token bar to a search warrant is what they're skipping in these cases. NSLs and related FISA warrants are extremely suspect. It makes sense that they would want to hide and obfuscate their use and existence. They're basically carte blanche for the government to inspect any communications they want - no justification required. The only reason they'd use them in place of a search warrant is because they are illegitimate.
This is absolutely not about terrorism, or threats. There's already a functioning-for-them (albeit broken in the legal checks-and-balances sense) system for that in the form of search and seizure warrants; they're trying to confuse you with the terrorism card.
This is a cover-up for an illegal power grab, nothing more.