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 BaldwinSeven Senate races to watch in 2022 Senate Democrats urge Google to improve ad policies to combat election disinformation Senate Democrats reelect Schumer as leader by acclamation  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.