“not all military interventions require congressional approval”
That depends on who you ask. You’ll get a different answer, for example, if you check for one in the Constitution, versus asking a lawyer or politician.
“I might agree that the events of 9/11 made such actions more palatable to the general public, but you can’t say they made them possible.”
At the least, it made politicians not really bother much to go through the motions anymore. At least when we decided to cross the border into Laos and Cambodia during Vietnam, without authorization, we tried to keep it a “covert” operation so we could deny our involvement. With Syria, we didn’t bother, everyone knew exactly what we were doing and we even held press conferences to boast about it.
The Constitution is pretty clear. Only Congress can declare war, but the president is commander in chief. Thus Washington called out the militia to suppress the Whiskey Rebellion, parts of the Barbary Wars were fought without congress, Reagan attacked Grenada, etc.