Howard Dean ran for president in 2004 as the outsider ready to battle an entrenched establishment in Washington. And so, four years later, did Barack Obama.

Now, one year into Mr. Obama's presidency, a sharp dispute between the president and Mr. Dean over the health care bill the Senate approved Thursday -- Mr. Dean denounced it as a sellout, while Mr. Obama heralded it as a historic breakthrough -- is illustrating the roots of the ideological breach within the Democratic party.

It is not just that the left wing of the party thinks that its centrists hold too much sway and are too quick to cave when faced with pressure from the right. It is also that this White House, stocked as it is...

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