It is amazing what a difference a serious primary challenge can make. Representatives in Congress who have serious primary challenges never seem to buck their party. The Politico wrote,
[F]inally, today's study in contrasts: moderate Sens. Michael Bennet and Blanche Lincoln, both of whom face tough races next year. Lincoln, the final hold out on Saturday, has threatened to withhold her support going forward. Bennet on Sunday candidly pledged to support the bill even if he knew it would cost him his seat.
What is the difference between Bennet and Lincoln? Bennet is currently facing a serious primary challenge from Andrew Romanoff, while Lincoln is not currently facing a primary challenge.
Romanoff is the former speaker of the Colorado House of Representatives. This gives him some statewide name recognition and a history of successfully running political campaigns, unlike the political novice Bennet. It is possible Romanoff could beat Bennet in a primary, so Bennet is worried about angering the Democratic base. Bennet claims that he will support health care reform, even if it could possibly cost him his seat, and this may well be true. But what Bennet left unsaid was that he knows opposing health care reform would definitely cost him his seat--thanks to his credible primary challenger.
We have seen the same pattern from Arlen Specter in Pennsylvania that we see from Micheal Bennet in Colorado. It is amazing how quickly a serious primary challenger turns a senator into a reliable vote on the important issues.