Trump says it for the same reason that Southerners of refinement and charm say: "Bless your little heart." Instead of: "My, you are quite the f***ing idiot, aren't you?"
I only support someone in the primary who doesnt have this pro-Jeb attitude.
Bless your little heart.
I'm stealing that line - it is now pretty high up on my all-time list of zingers.
FYI, on the same topic, check out #30.