Former Wisconsin Gov. Tommy Thompson leads the pack for the GOP Senate nomination, according to a Public Policy Polling survey. However, his lead is anything but stable.

Thompson led with 35 percent, followed by former Rep. Mark Neumann with 29 percent and state Speaker Jeff Fitzgerald with 21 percent.

PPP, a Democratic survey firm, also showed that Thompson has 86 percent statewide name recognition, which underlines the shakiness of Thompson’s slim margin.

Even before Thompson announced that he was filing papers to run for Senate, the Club for Growth aired a TV advertisement attacking Thompson’s record, and the group’s president, Chris Chocola, has been harshly critical of Thompson’s fiscal record.