In the olden days, the Democratic Party Machine was the major source of funding and was able to impose party discipline.
Those days are long gone. Unless Citizens United is scaled back, it'll get worse. Who needs a party if you have your own billions or your own billionaire to spend $100M to get elected?
What can Obama threaten them with? He's not an LBJ with secret millions to pass around from the White House. He's not going to get Joe Manchin to suddenly be a progressive no matter how many speeches he gives.
And it's not working out all that great for the Republicans these days, either. They have the iron discipline, but their Purity campaign is destroying their ability to become more popular and have more votes in the future. Imagine a Democratic Party with iron discipline that was headed by Joe Lieberman... :-(
It's going to continue to be a rough slog until the Republicans are crushed and no longer hold leadership. Obama can't do that on his own....
Sorry if I seem preachy on this stuff. I appreciate the arguments. :-)
Cheers,
Scott.