Well, I don’t know about SWAT teams, but we do have standing armies, don’t we? The Constitution is clear, “raise and support Armies . . . maintain a Navy.” It seems we pretty much kept to it until after WWII.
If I were president I would have our troops guarding our borders.
My point is that SWAT teams are equivalent to standing armies - some have armored vehicles. I understand they are not at the federal level.