More big gains for House Dems in 2008? That's what a comprehensive new poll by a Dem firm finds.

A new poll just out from Democracy Corps — the Democratic polling/consulting firm run by James Carville and Stan Greenberg — finds that Dems are poised to pick up a new batch of House seats next year, even as the number of vulnerable Dem seats dwindles.

The poll — which was conducted in 70 competitive districts, half held by the Democrats and half by the GOP — finds that the most vulnerable Democrats, who come largely from the ranks of freshmen who picked up Republican seats last year, are not in any great danger. "Democrats are ahead in their most vulnerable seats by 10 points, 51 to 41 percent, leaving the Republicans with few pickup opportunities," the pollsters say.

Meanwhile, Democrats lead in the most competitive tier of Republican-held seats, as well as in the second-tier trouping of vulnerable GOPers — meaning there could be vulnerable Republican seats even outside of the 35 tested. "This pattern that allowed the Democrats to take 30 seats in the last mid-term election could well take Democrats up to 20 in the Presidential, unless confounded by intervening events," the firm writes. "There really could be another wave election."

A 20-seat gain by Dems would bring their total to 253.