MADISON, Wis. -

Democratic U.S. Senate candidate Tammy Baldwin said an ad being run by her Republican opponent Tommy Thompson questioning her support for victims of the Sept. 11 terrorist attacks is "desperate and dishonest."

Baldwin was asked about the ad at a news conference Thursday where she received the endorsement of the Wisconsin Professional Police Association. The statewide police union had endorsed Thompson in 1994 and 1998 in his runs for governor.

Thompson's 9/11 ad faults Baldwin for voting against a 2006 resolution in Congress honoring victims of the attacks. Baldwin said she voted against it because Republicans added other language she couldn't support.

The Wisconsin Professional Police Association said that although it has supported Thompson in the past, his current campaign "has an extremist tone."

"Tammy Baldwin clearly demonstrated her support for public safety. Time and time again, she has fought to increase law enforcement first-responder funding to have the resources people need to keep people safe," said Jim Palmer, executive director of the Wisconsin Professional Police Association.

Baldwin issued a response ad faulting Thompson getting paid $3 million after heading a private company that won a government contract to help first responders in the attacks.

On Thursday, Thompson was endorsed by the Milwaukee Police Association. The group said Thompson has demonstrated consistent support for public safety and effective government.

Thompson and Baldwin will square off again Friday night at their third and final debate.