The "super PAC to end all super PACs" is headed to South Dakota.

Mayday PAC, a group that is trying to curb the influence of money in politics, is launching a $1 million effort to support underdog Democrat Rick Weiland in the South Dakota Senate race with four weeks to go until the midterm elections, the group announced Tuesday morning.

It's a sizable investment in an inexpensive state which is considered to be among Senate Republicans' three best pickup opportunities. Polls show former governor Mike Rounds (R) leading the open seat contest comfortably. Larry Pressler, a former Republican senator running as an independent, is also in the race.

Mayday PAC is kicking off its effort with a new ad touting Weiland as crusader against "big money."

Mayday PAC released this ad in support of South Dakota Senate candidate Rick Weiland (D), who it says will "take our country back from big money." (Mayday via YouTube)

“Rick Weiland is running for U.S. Senate to take our country back from the big money that controls our democracy. He believes all of us -- farmers, ranchers, workers, families -- deserve a fair shake," says the narrator.

Mayday PAC is the brainchild of Harvard law professor Lawrence Lessig and GOP media strategist Mark McKinnon. The group's goal is to curtail the influence of money in politics by electing candidates committed to reforming campaign finance laws.

"Embrace the irony," Mayday PAC says on its Web site. The super PAC surprised many observers when it surpassed a fundraising goal this summer.

The super PAC has experienced mixed results so far. In House races, it is backing Rep. Carol Shea-Porter (D-N.H.), Rep. Walter Jones (R-N.C.), Iowa Democrat Staci Appel and Arizona Democrat Ruben Gallego. All remain in contention.

For the Senate, aside from Weiland, it backed New Hampshire Republican Jim Rubens, who lost in the primary.