MARK KIRK CAN’T SEEM TO HELP HIMSELF…. Rep. Mark Kirk, the Republican Senate nominee in Illinois, seems to have trouble telling the truth — about much of anything.

His wildly exaggerated claims about his military service keep piling up. His exaggerated claims about foreign policy suggest he doesn’t really understand his signature issue. And now Mark Kirk seems to have been caught exaggerating his background as a classroom teacher.

Representative Mark S. Kirk of Illinois, a Republican candidate for the United States Senate, has often reminisced about his time as a teacher.

On the floor of the House, in campaign commercials and during interviews, Mr. Kirk has invoked his experience in the classroom. At a speech this spring to the Illinois Education Association, Mr. Kirk declared, “as a former nursery school and middle school teacher, I know some of what it takes to bring order to class.”

A review of public comments that Mr. Kirk has made over the last decade shows that while he may refer to himself as a former teacher, he does not talk about the brevity of his experience: a year in London at a private school and part-time in a nursery school as part of a work-study program while he was a student at Cornell University.

In this case, Kirk didn’t just make up tall tales out of whole cloth, as with the case of his military service. But when it comes to his teaching background, Kirk seems to have exaggerated his career to the point of misleading the public. Again.

In fact, in arguably the most entertaining anecdote, Kirk delivered a speech on the House floor in 2006 about school safety. He reflected on students he remembered who “bore scrutiny as people who might bring a gun to class.” Yesterday, Kirk’s campaign spokesperson said the congressman was referring to nursery school students in Ithaca.

Now, I’ve never been to Ithaca — maybe it’s a much tougher place than I realize — but I have a hard time believing that Mark Kirk worried that children in a nursery run by a United Methodist ministry in 1981 might be packing heat.

At this point, Kirk’s record of exaggerations is so extensive, practically every claim he makes about any subject should be considered suspect. He’s simply proven himself to be untrustworthy.

As a friend of mine joked this morning, “The only thing Mark Kirk hasn’t claimed at this point is that he commanded the Starship Enterprise.”

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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.