Ft. Lewis would definetly be a stupid place for jihadist to try and hit. Two others that would be equally insane would be Coranado, CA and Little Creek, VA. The Teams would not take to kindly to that.
The interesting thing about all the SpecOps folks is that they are always in close proximity to a weapon (usually a firearm) of some sort. There would be no need to rush to an arms room or find somebody to open one up. Even that wouldn't prove too hard.
I remember about ten years ago, there was a big story in Tacoma about a Ranger sergeant that had moved into a drug neighborhood with lots of gang activity, and they decided to go ummmm "Hollywood" and clean the place out. SO they checked out a couple of SAWs and an M60 and some M4's and laid an ambush, AFTER warning all innocent residents to clear the soon to be FREE-FIRE zone.
The news stories said something like 3 or 4 THOUSAND rounds of ammo was expended. OOOOPS! Embarrassing point. No KIA's. Nobody hit at all. Those guys got into trouble but I think they caught more grief for their lousy marksmanship. If you're gonna do it....do it right!