He doesn't have to be more liberal, just communicate it better. Kerry was pretty far to the left economically, he just couldn't shake the elitist image.
Kerry was moderate to center-right economically. Even the most left wing candidate - in my opinion Feingold, is barely left leaning. The Democratic party is simply not a center-left party, as its base would like to believe, or a far left party, as FOX would have it - no, it is a moderately, center-right party, beholden to corporate sponsors.
Interesting observations. What kind of weed are you hittin?