Before supporting any candidate, I believe one should do this thought experiment.

[peggysue2]

23. Likability

Group 1--Bill Clinton: It's the economy, Stupid and I feel your pain; GW: they guy you'd like to have a beer with, compassionate conservative; Barack Obama: Yes, we can, perceived as The One; Donald Trump: appeals/appealed to the those left behind in the global economy, a self-proclaimed billionaire with a Barnum & Bailey presentation, Only I can solve your problems.

Group 2--Only John McCain had the spark of likability, the renegade. But even that was diminished once he ran and chose the ridiculously uninformed Sarah Palin as a running mate. Sadly, Hillary Clinton was savaged by right and left-wing smears and innuendo, enough that her likability went well underwater. Same with Al Gore. Bob Dole and Mitt Romney were perceived as flat, stiff personalities, not terribly likable.

So, my current choice of Joe Biden as our nominee falls into Group 1. Say what you will about Biden but he is manifestly likable to a large swath of the Democratic electorate, even with his warts and flaws. And likability holds a mysterious sway over voters, that need to identify with a candidate on a personal, emotional level. Biden does the personal, emotional stuff easily because it's part of who and what he is.

Is that the only factor? Of course not. Just one more thread in voting preferences, IMHO.