Politics is a tug of war with conservatives pulling the country to the right and liberals/progressives pulling the country to the left. It's the activists on both sides who pull the hardest with the rest of the country lending support to one side or the other. There are disagreements on the left as to how we should play this game.
DLCer's argue that we should get the country to center or just right of center and then stop trying to gain ground while trying not to lose ground. That strategy would only make sense (if at all) if the conservatives would stop pulling to the right. But there is no voice on the right telling them that center or JRofC is acceptable. They will see us a giving up and redouble their efforts to pull the country to the right.
The only winning strategy is for liberals/progressives to pull to the left as hard as they can and never stop. It's not up to us to decide how far left the country should go, it will go left until enough of the American people stop supporting us and start supporting those on the right.
How does this translate into upcoming elections? Both sides will nominate candidates that they think will pull the country left/right as far as the general public will allow them to. If Guilianni is the republican nominee, that says something about how far right the conservatives think the country is willing to go. Conversely, if Hillary is the democratic nominee it says the same about liberals/progressives. Neither candidate is more than a micron from the center.
I would love to see the left nominate John Edwards (for example) and the right nominate someone like Huckabee. Now that would be a battle!