Thompson had long led in the polls, but has problems with his conservative bona fides: He is on record as having supported a national healthcare plan with an individual mandate, the centerpiece of Democrats' healthcare reform law, and while he opposed the law he worked early on with former Sen. Tom Daschle (D-S.D.) to craft a bipartisan framework. He also increased public employee pensions during his time as governor.

The primary is just a few weeks away, on Aug. 8. If Hovde can maintain his trajectory, he'll be the odds-on favorite, although if deep-pocketed conservative groups backing Neumann, like the Club for Growth and Senate Conservatives Fund, go on the attack against both Thompson and Hovde the field could once again muddle in a hurry.

The winner of the primary will face Rep. Tammy BaldwinTammy Suzanne BaldwinManaging the US dollar to pay for congressional infrastructure plans Duckworth, Pressley introduce bill to provide paid family leave for those who experience miscarriage Senate Democrats call for Medicaid-like plan to cover non-expansion states MORE (D-Wis.). PPP's poll shows both Thompson and Hovde in a statistical tie with her.

PPP polled 1,057 Wisconsin voters, with an an oversample of 564 usual Republican primary voters, from July 5-8. The primary poll had a margin of error of plus or minus 4.1 percentage points, while the general election polls' margin of error is plus or minus 3 percentage points.