He is saying that Democrats who work to kill or minimize the public option will be primaried:

Former Democratic National Committee chair Howard Dean fired one of the clearest warning shots at hesitant Democratic lawmakers on Thursday, insisting that if the party was unable to produce a health care bill with a public plan, there would be electoral consequences.

“I do think there will be primaries as the result of all this, if the bill doesn’t pass with a public option,” Dean said, in a phone interview with the Huffington Post.

The essence of the problem is that no one fears the people, the majority of the people who favor real healthcare reform, and it has to be more than primaries.

We have to be willing to support Green Party candidates and the like in the general election against the most egregious of the Blue Dogs in the general.

If we lose 4-5 seats this way, it will move 40-50 allegedly Democratic Party votes in our direction in Congress.

We can see the effects of real challenges to incumbents in the voting patterns of Arlen Specter, which have become much more loyal since Sestak decided to run against him in the primary.

Right now, there are no consequences for DINOs who actively oppose core party values.