Add this to Tommy Thompson’s growing list of gaffes.

During a June 4 speech to the Lake Country Area Defenders of Liberty, the Wisconsin GOP Senate candidate forgot the date of the most devastating terrorist attacks on American soil. Oops.

While ironically attempting to stress his experience in Washington as the Health and Human Services Secretary during the George W. Bush administration, he mentioned his responsibility he held after the September 11 attacks:

“And then after 9/18, I was responsible for the public health of all Americans, responsible for preventing any attack using weaponized medicines like the plague, like smallpox, like anthrax, like tellurium. And I was responsible for all that. So there’s hardly anybody that has the knowledge or the base of knowledge that I do. If you want a conservative that can change things around, that is going to make the tough decisions right now, you want me, and I make no bones about it.”

Today, the Huffington Post contacted the Thompson campaign, and spokesman Brian Nemoir had this to say:

“There are two plausible explanations as to the recent 9/18 versus 9/11 reference made by Tommy Thompson at a recent event. First, the entire civilized world has the wrong date of this historic and tragic attack on our nation’s soil; second, during a spirited campaign appearance Tommy Thompson misspoke regarding an horrific episode in our country’s history during which he played a key leadership role. The campaign is fully examining both scenarios.”