Updated: Oct. 22, 10:24 a.m.

MoveOn.org Political Action, the Democratic grass-roots group known for its attacks on Republican candidates and President George W. Bush’s policies in previous elections, is back with a vengeance. With the help of its more than 4 million members, the group is taking out ads in eight Senate and 20 House races across the country.

The ads, like the one viewable below that will run in support of Rep. Steve Kagen (D) in Wisconsin’s 8th district, feature still photos of members decrying the Republican candidate’s support from conservative front groups and urging support for the Democrat. In the Wisconsin race, the Republican nominee is roofing contractor Reid Ribble.

“Reid Ribble is backed by front groups who won’t reveal their donors. So with MoveOn’s help, real voters got together to make their own ad with one simple message: If Reid Ribble’s on their side, he sure isn’t on ours,” the narrator says. “Vote Steve Kagen!”

Ribble has received support from a number of outside groups, including the anti-abortion Susan B. Anthony List. However, the AFL-CIO and American Federation of State, County and Municipal Employees have both made independent expenditures on Kagen’s behalf, and both House campaign committees have spent money in the northeastern Wisconsin district.

MoveOn once was a favorite target of Republicans complaining about outside spending on the left, but this year, group spending in favor of GOP candidates has drawn Democrats’ ire from the White House on down.

MoveOn officials said the group will run ads “at heavy rates” in the Illinois Senate race, where Democratic state Treasurer Alexi Giannoulias faces Republican Rep. Mark Kirk, and in Virginia’s 5th district, where freshman Democratic Rep. Tom Perriello faces Republican state Sen. Robert Hurt. MoveOn members voted Giannoulias and Perriello among their “Progressive Heroes.”

MoveOn is also running ads in the California, Colorado, Illinois, Pennsylvania, Ohio, Nevada, Missouri and Washington Senate races. Each of those eight races is either an open seat or features an embattled Democratic incumbent. In Pennsylvania, incumbent Sen. Arlen Specter (D) lost the primary.

The same is true, to varying degrees, in the 20 House races. Targeting districts in 14 states, MoveOn bought ad time in two districts each in Florida, New Hampshire, New Mexico, New York, Pennsylvania and Washington.

The group won’t be helping Democrats who voted against health care reform, one of its signature campaign measures over the last year.