OK, this is an extremely weird and scary story that points to a deeper conspiracy. I can totally see congressional offices having panic buttons. It's common for any secure type place like a bank.
Pressley states the button was there for for an earlier security drill. Then it's gone. Why? It's not like some hi tech piece of gear that would need replacement.
Who removed it? Why? When? In theory, if there was some legit reason to remove it there would be a work order somewhere and a whole chain of paperwork. After all, I don't think people can generally just walk in to a congressional office and and start installing or uninstalling stuff.
Someone wanted this conflict and possibly they wanted casualties. I smell an FBI entrapment operation operation. In the past I would have never thought such a thing, but with the FBI's entrapment of Flynn and others thru the creation of forged evidence, all bets are off as to how far they might go.
Oh, somebody must have watched Designated Survivor.
Why not, the Awans did... and Xavier Becerra made a computer disappear.