There's a good reason for this, as Tapper points out: "Many of them -- and other Democrats in competitive districts -- are fighting for their political lives in a harsh environment and have found it necessary to distance themselves from their leaders and Democratic policies."
In other words, despite what Pelosi and all may be saying about fringe Tea Partiers being the only ones upset about the state of things, Democrats on the ground know they're in trouble and are responding accordingly. Tapper's got a nice collection of ads illustrating his point. While I get a kick out of Alabama's Bobby Bright actually calling himself an "independent conservative," I think the spot for Pennsylvania's Jason Altmire skirts the edge of genius when it stokes anti-immigration-reform sentiment and anxiety about China in one brief turn of phrase. One voter in the spot praises Altmire for "making sure the border fence was built with steel made here, not China." Two-fer!