Solidarity and the Conventional Wisdom
What makes L'affaire Booker a real problem rather than a passing mis-step, is that all intra-party criticisms from the right are taken by the media (which decides all presidential elections) as validating the Republican philosophy.
This is why I was so F'ing mad at Obama back when he was playing at deficit hawk. He was legitimizing the Republican viewpoint.
It is basic economic fact, supported by all evidence, that reducing the deficit in a down economy is terrible policy, and can easily result in an even higher deficit.
But if ALL Republicans and SOME Democrats think X then the media will accept X as the centrist position and presumptively correct.
If ALL Republicans and a HANDFUL of Democrats support restricting reproductive choice then restricting choice is the BIPARTISAN position, and thus must be correct.
As long as there is one talismanic Democrat (Zell Miller, Joe Lieberman, etc.) taking the Republican side then the Republican side is VINDICATED in the eys of the media chowder-heads who decide all American elections.
The Republicans understand this, which is why they will destroy Republicans who get off-message.
Now criticism of Democrats from the left... that is actually net-helpful. The only downside is that some hippies may be dissuaded from voting, but the upside is that the Democratic Party is self-SistahSoldiering. The Democratic Party spends half its time distancing itself from its own bases, which the media chowder-heads admire.
POSTSCRIPT: It is delightful that DU spell-check tries to turn "sistahsoldiering" into "testosterone." True story.