I note that Mardi Gras is deeply associated with the Catholic/Christian tradition (prior to the Protestant movements). Yeah, "Get all your sin in before lent starts."
I've always thought that two or three Israel-style suicide bombers hitting malls and amusement parks would have a tremendous impact, and would be very do-able. The nightmare is, of course, a nuke detonated on a container ship in one of our big harbors.
I was engaging in rank speculation. Since I was speculating here are my thoughts on Olympics and amusement parks. I do not think the Olympics will be a target. Somehow I think that they will choose something less defended and go for more of an element of surprise. The nuke aboard some ship is of course the biggest danger and IMHO there is not a whole lot going on that would stop that. Along more conventional lines I was thinking of a ship containing a hazardous cargo being rammed nto a stionary target as a hypothesis. For New Orleans maybe a barge or freighter ramming a Levee and then detonating breeching the levy and letting the Mississippi do the rest of the work. The other targets mentioned all have some gas/petroleum distalate storage facilities that are vulnerable. new York City area includes the Port of Elizabeth, NJ.
Stay well - Stay safe - Stay armed - Yorktown