Nitpicker has received confirmation from the DOD that Rep. Mark Kirk had violated Pentagon policy by conducting partisan political activity while on active duty. The statement from AF Major April Cunningham:
In December 2008, Commander Kirk, while on active duty, participated in video discussions in the media about the unfolding situation involving then-Governor Blagojevich of Illinois. Members of the Armed Forces on active duty may not participate in television discussions as an advocate for or against a partisan political party, candidate, or cause.
In July 2009, while on active duty in the Washington area, either Commander Kirk or a staff member posted a "twitter" to his Senate campaign web site that indicated he was on duty at the National Military Command Center. At the time, Commander Kirk was a candidate for the Senate. Candidates for political office may not participate in any campaign activities while on active duty. They may not update or revise their websites, and they must inform their campaign staff of the applicable restrictions.
Department of Defense Directive 1344.10, Political Activities by Members of the Armed Forces, addresses these matters.
Commander Kirk was counseled about each of his violations after they occurred and signed a statement acknowledging the limitations on his ability to participate in campaign activities while on active duty. He was required to complete this acknowledgement before being allowed to begin active duty in December 2009.
Kirk's allegation that the Obama administration "changed the original language of the waiver, inserting concerns about his 'partisan political activities'" seems debunked now. It's pretty hard to imagine that they required him to sign a waiver acknowledging that he know he wasn't supposed to politic on duty because he had politicked on duty, and the phrase "partisan political activities" never appeared on that waiver.