Christopher is pretty much on point here; it's not something you can actually "learn" you either have it or you don't (though some semblance of it can be learned & developed over time). I pointed this out yesterday on some forum I was visiting, showing how Colin Keys, a far less creative and technically skilled showman, managed to go so far on AGT vs. Kevin James, a master showman and one of magic's leading innovators -- Kev is an awesome dude but let's face it; he's never been that bouncy, fresh faced, cocky youth; Kevin's "confidence" comes from a different place than Colin's and certainly not rooted in the sex appeal factor that Colin manipulates quite well. . . it will come to haunt him by the time he hits middle age, possibly sooner (I got lots of breaks as a cute kid but once hitting my 20's vs. my teens, the opportunities simply weren't as abundant e.g. young & cute and full of energy is one aspect of Charisma, but it MUST BE accompanied by pure confidence, which frequently looks like cockiness.)
Harry Anderson was Charismatic as is Ricky Jay, neither of them on the "catch of the day" list but they both radiate a unique sense of charm THAT WORKS FOR THEM. . . this is the other side of Charisma; knowing who & what you are but more so, being comfortable in that persona (not being comfortable is the biggest reason so many people fail over and over again in life; something I've learned the hard way).
Barrack Obama is Charismatic as was Adolf Hitler, but why?
Both of them are cheerleaders! Ignore the darker side of Hitler's reign and look at all the good he did for the German people and bringing Germany itself, from the brink of total devastation on multiple levels. Most historians agree that had he stayed put and not gone after Poland and subsequent conquest and had he been more positively supportive of creating a Jewish state (other the state of non-existence) he would have most likely won the Nobel Prize and gone down in history as one of the greatest political leaders of the early/mid-20th century; especially when you pause and recognize that a large percentage of British, American and Canadian industrial leaders and political personalities were more supportive than not, even embracing some of the early policies of the man. But this is stuff we rarely hear about.
Obama gave this nation a unique sense of hope but in so doing, became a sacrificial lamb. Yet, as an orator, he's one of the best spoken and commanding politicians that's been seen in decades if not generations; like him or his policies or not, we must give him kudos in this area. It is this sense of confidence and seeming connection with "the people" vs. those "people" dressed in corporation clothing, that makes him "more", formidable and appealing. In my memory the only other activist/politician that lived up to this standard was Bobby Kennedy (Reagan don't count in that he was a train B-rate Actor. . . as Bob Hope frequently pointed out).
Confidence or "KNOWING" as one of my acting coaches used to say, is the real key; high energy enveloping that confidence and idealism are the other ingredients.
Charisma within show biz frequently gets confused with sexual/sensuality, which is why the late 20th and early 21st centuries have fewer "legendary older actors" on the screen and more so, fewer that don't have a sculpted physical shape about themselves. but look at Gov. Christ Cristis. . . he's FAT and still charismatic. . . Albert Goshman wasn't just fat, he was a slob that people just loved; they loved him enough to ignore the food and stains on his shirts & ties and so he went down as one of the greats.
I guess "figuring out" the idea of charisma is as big a challenge as figuring out the idea of God, Love, or (according to my various heterosexual friends) women. . .