We need more than Dem voters to win in the fall...But we don't have to move further right to get 'em
The largest bloc of voters are people who are alienated from the existing politics:
People registered as "independents", or people registered as Democrats or Republicans who no longer feel any intrinsic trust in their own parties.
Terms like "experience" no longer mean anything to such voters, because they have no respect for any part of the existing order in this country.
A center-left or left message will more likely resonate with voters than a "center" message, so long as we present it as clear, strong leadership. Centrism and "moderation", to the electorate of 2016, means not standing for anything and not having any core values at all. It reads as "not giving a damn".
The voters are going to prefer a candidate who talks about big change, who expresses the idea that it is worthwhile to try to build an entirely different model for this country than what we have now. Wherever they are on the spectrum, most of them don't see what we have now as salvageable.
Whoever we nominate, the voters will want to hear about "action" much more than now-meaningless terms like "experience".
They won't elect anyone who brags about being part of the status quo.
Only a candidate who embodies this spirit of rebellion, who can channel it in a positive rather than destructive direction, can win as a Democrat in 2016. Any other approach dooms us to an Adlai Stevenson-in-1956 or Pat Brown-in-California-in-1966 pasting.