In the generic congressional ballot, voters would choose Democrats by a factor of 40% to 29%, but more than a quarter of those surveyed are still undecided, a new Zogby International poll shows.

However, while they still hold a big advantage over the GOP, Democrats get support from barely half of those asked whether "Republicans deserve to retain control of Congress, or is it time for the Democrats to take over and run things?" Just 30% said they think Republicans deserve to stay in charge.

Pollster John Zogby: "Paint me as one who is not sure we're going to have a landslide. We may, but the results are too mixed right now to say for sure."

Update: The new AP poll shows Democrats leading by 20 points, 52% to 32%.