the only thing he brings to the table that no one else really has is not just security credentials, but military credentials. sure, kerrys' got some of that, but the same way that cleland had it. no one can touch clark, and he wouldn't go down on that issue like cleland did or kerry will (just my speculation. i love kerry)
besides that, its mostly the combination of assests he brings. he's articulate like edwards, but he's straight-spoken like dean. He gives some amazing interviews and is quick to his feet. check out his performance on crossfire.
http://mirror1.draftclark.org/video/2003/06/25/Clark_Crossfire.mpghe's handsome, something that is important. sure, dean's kind of handsome, kerry used to be, and of course edwards is, but clark has it too, along with being a man in a uniform (btw, i'm a straight male, and this assessment is purely objective and for the purposes of political analyzation only).
he's also a southerner. so's edwards, and to a lesser extent graham (only parts of florida can be considered the south, and while graham is a true southerner, he's not from a true southern state). arkansas is a swing state, and one could argue that he's more likely to win arkansas than edwards is to win NC, especially with lincoln on the ballot as well (hopefully huckabee's declining to run will dampen gop turnout).
the title "general" carries with it a lot of weight. people need to feel comfortable and secure, and a general certainly does it. no one can attack him for his "inability to lead" or "stature." he led not just the US to victory, but all of NATO. he won a war, for fuck's sake, all with the loss of one american life.
2 questions remain: can he light up a room like clinton, convincing people who wanted to sabotage his campaign instead to eat out of his hand? probably not. but he'll still need to wow the rest of the uncommitted interests. luckily, with probably 7 candidates dropping out in the next 6 months, that will free up a lot of support that will then go on the market looking to endorse someone else. can clark convince them that he's their guy? not sure.
also, can he govern? no question that he can lead, but as truman said after eisenhower's inaguration, ‘‘Poor Ike. All his life he has told soldiers ‘Do this, do that’ and his orders have been carried out. Now he’ll do the same from the Oval office and discover that his commands are not always fulfilled’’. although that didn't exactly happen with ike, may that prediction fully realize itself with clark? we'll find out.