MILWAUKEE -

The four Wisconsin Republicans running for U.S. Senate are remaining cordial in person, even as their television campaigns are getting increasingly negative.

The four candidates appeared Wednesday at a forum in Milwaukee. They took the stage separately for 30-minute presentations.

The four are hedge-fund manager Eric Hovde, former Wisconsin Gov. Tommy Thompson, state Assembly Speaker Jeff Fitzgerald and former U.S. Rep. Mark Neumann.

Each discussed his qualifications, and they avoided any personal attacks.

However, Neumann released an ad Tuesday criticizing Hovde's conservative credentials. Hovde responded Wednesday with an ad accusing Neumann of slinging mud in an attempt to distract attention away from his own poor record.

Neumann said Republican leaders had asked him to follow party lines and vote for a pork-laden budget even though they didn't explain where the money was coming from.

Neumann said he voted against the bill, even after fellow Republicans warned him a no vote would end his career. He told business leaders at Wednesday's forum that what actually happened was, his example helped usher in a new era of fiscal restraint.

Hovde said that as a U.S. senator, he would reform the tax system, fight for broad deregulation and encourage the oil and gas drilling technique known as "fracking."

Hovde is a political newcomer with deep pockets. He has already put $4 million of his own money into his Senate bid.

At a candidate forum in Milwaukee on Wednesday, Hovde said the government cannot continue to mismanage its finances and needs to significantly reduce regulations and stop the Federal Reserve Bank from monetizing the debt.

Thompson said his strong political experience makes him the U.S. Senate candidate with the best chance to win this fall.

Thompson served as Wisconsin's governor for 14 years and also secretary of the U.S. Department of Health and Human Services.

At a candidate forum Wednesday in Milwaukee, he said that his unmatched experience means he could go to Washington and get to work right away on extending tax cuts and repealing health care reform, whereas his rivals would still be looking for the restroom.

A poll released last week showed Thompson leading the Republican field with 35 percent support. Hovde was second at 23 percent.

Fitzgerald said he would bring the same conservative leadership to the U.S. Senate that he has shown in the state Legislature.

Fitzgerald, the state Assembly Speaker, said Wednesday he helped balance a $3.6 billion state deficit without raising taxes, he helped pass a concealed-carry bill and he defunded Planned Parenthood. He said he already proved his political courage.

A recent poll found Fitzgerald's support in the single digits, and he also trails in fundraising. He said he hopes the front-runners will continue to attack each other, creating an opening for him to attract voters.

The four Republicans square off in a primary on August 14. The winner takes on Democratic U.S. Rep. Tammy Baldwin in November. 

Meanwhile, the Democratic Party of Wisconsin is calling on the four Republican candidates for U.S. Senate to release their tax returns from the last 10 years.

Candidates aren't required to do so. However, Democratic Party chairman Mike Tate said Wednesday they should be transparent about how they made their money and about how much they'd benefit personally from the tax cuts they support.

Baldwin, the lone Democrat running for the Senate seat, released the last 10 years of her federal and state tax returns in May.