NOW THERE’S A STRONG CAMPAIGN SLOGAN…. In June 2009, Rep. Mark Kirk (R) of Illinois was one of just eight House Republicans to break party ranks and support the American Clean Energy and Security Act (ACES), which included a cap-and-trade system. Far-right activists, who believe overwhelming evidence pointing to global warming is a communist conspiracy, vowed revenge.

Exactly one month to the day later, Kirk, fearing a primary loss as he ran for the Senate, reversed course and announced his opposition to the bill he’d just supported.

Kirk, whose reputation for borderline-pathological dishonesty is well deserved, has never fully explained why he voted for legislation he disagrees with. This week, a voter pressed Kirk on this point.

At a town hall meeting [Thursday], Kirk was questioned about his position on cap-and-trade legislation, which he voted for in the House, but has pledged to oppose if he’s elected to the Senate. Kirk defended his reversal, explaining that he supported the bill out of “ignorance” and “lack of understanding” of the economy:

“We make a lot of errors in Congress, not out of malice or corruption. It’s out of ignorance and lack of understanding of how a $14 trillion economy operates,” Kirk said.

I suppose there’s a refreshing quality to candor like this, but in the midst of an extremely close Senate race, it doesn’t exactly seem like a winning message: Vote Kirk, he supports sweeping national legislation without getting his facts straight.

It wasn’t like this bill snuck up on him. The ACES legislation followed an extensive House debate, in which Kirk was confronted with plenty of arguments on both sides. It was his job to evaluate the information and choose wisely. Given the quality of the bill, Kirk made the right call.

That is, until Kirk decided he was for it before he was against it, and only voted the way he did because of “ignorance” and a “lack of understanding.”

I’ll give Kirk a B+ for candor, an F for competence, and a D for judgment.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.