When you're just some senator or congressman, or governor or mayor, you're always free to criticize the party over anything.  We need disparate voices, challenging voices, we're a big tent, all that.

BUT.  The moment that you accept a presidential or vice presidential nomination, you also agree to represent the entire party, and the unspoken agreement is, you will do it for the rest of your life.  It is no small thing for 40 some million Democrats to invest their hopes in you.  In exchange for that support, we ask only one thing.  Win or lose, you will spend the rest of your life staunchly defending the party, laboring to get Democrats elected wherever you can.  You can leave the moralizing, the deal breaking, and what have you to the next generation of young Turks.  You have just graduated to Senior Statesman.

That's why Democrats love Teddy Kennedy.  It's how Bentsen wound up in the Clinton administration.  It's how Dole survived Ford.  None of those men ever shat on their friends.  They danced with the girl who brung them.

Not Joe.  Somehow he thinks that he can return to his cozy position as the Grand Poohbah of Centrist Scolding.  

It doesn't work like that.  We get one chance every four years to nominate two people.  If you accept our invitation, you owe us your blood sweat and tears.  Now and forever.  If you can't life up to that, fuck you.  You're gone.