The Woman in the Middle

Rep. Ellen Tauscher (D-Calif.) says she takes seriously the threat against her from the Democratic Party's liberal base. (By Lucian Perkins -- The Washington Post)

But Kos points to Harman as a perfect example of how the Net roots can keep Democrats in line. He said Harman used to be a constant irritant, a go-to quote for reporters looking for a Democrat to tweak liberals -- until she had to fight off a primary challenge from the left in 2006. "She's been great ever since," he said. Now Harman even writes on the liberal Huffington Post blog.

Kos can imagine a day when Tauscher still holds her seat but is no longer distasteful to the left. "That's what victory would look like -- a more responsive representative," he said. So when Tauscher praises Pelosi as "perfect on substance, perfect on optics," it's hard to know if that's a result of personal evolution, political trends, or blogospheric pressure, but it's music to Kos's ears. It's helpful to Democratic leaders, too.

Said Rosenthal, the Working for Us founder: "We want them to understand what we're doing helps and enhances the majority."

But Pelosi still faces two potential dangers.

She could work so hard to appease the moderates that she alienates her base. In fact, the left blogosphere is already grumbling that Democrats aren't doing enough to stop the war. And there's always the left cliff. Those moderate first-termers could be one-termers if Pelosi overplays her hand.

"Nancy knows our majority is fragile in its newness," Tauscher said. "If you keep our most endangered species in your frontal lobe, you know what you have to produce."

Staff researcher Madonna Lebling contributed to this report.