CLT is a very valuable fortress hub (pretty much the crown jewel, so to speak) and as such probably the only US hub that's guaranteed safe in a merger.


EDIT:
Basically, here are US's hubs sorted from safest to most likely to be gutted:
CLT
DCA
PHX
PHL

Same for AA:
DFW
MIA
ORD
LAX
JFK/LGA