The Republican, now battling for a second term in a tight race in Illinois, stayed in the United States during the Iraq War when he served in the Navy Reserves. But on a public webpage on his official campaign website touting his record on veterans' issues, Kirk was listed as a "veteran of the Iraq war."
While Kirk campaign officials said it was a staff error, the issue resembles the controversy that nearly caused his 2010 Senate campaign to implode. Moreover, Kirk is now running for reelection against Democratic Rep. Tammy Duckworth, a military veteran who lost both of her legs during combat in Iraq.
Kirk campaign officials said the webpage was not meant to be made public, saying that it was supposed to be a private site while edits were being made to the page.
Campaign officials said a third-party vendor had drafted the language that they said had not been vetted or reviewed by the senator's staff. The language, they acknowledged, was inaccurate, saying it would be changed when the campaign began a more direct push to court military veterans.
After CNN inquired about the statement, the campaign moved the webpage behind a password-protected firewall. It had been accessible publicly and through Google searches about Kirk's work on veterans issues prior to that.
Kirk campaign manager Kevin Artl downplayed the error -- and instead attacked Duckworth over her tenure leading the Illinois Department of Veterans Affairs.
"Rather than focus on draft web copy that has yet to go through an approval process, we would welcome the media's attention on the six military veterans who died waiting for care during Tammy Duckworth's time at the Illinois Department of Veterans Affairs," Artl said.
Duckworth campaign officials declined to comment.
In 2010, Kirk came under heavy criticism for making a number of inaccurate comments about his military record, including falsely asserting he was the lone member of Congress to serve in Iraq and had been named the Navy's intelligence officer of the year. He later backtracked, including by saying he served "during" the Iraq war -- not "in" the war. He also later acknowledged that a different award was given by the Navy, and it was awarded to his entire unit.
Kirk apologized for his misstatements, including one saying he had been fired on in 2000 while flying reconnaissance missions over Iraq and another saying he was a veteran of Operation Desert Storm in the early 1990s.
During the Iraq war invasion of 2003, Kirk was a congressman representing a district encompassing suburbs north of Chicago. He served in the Naval Reserves at that time but was working stateside, even joking to a reporter in 2003 that he wouldn't see combat unless the Iraqi army came to Washington.
After a 23-year career in the Navy Reserves where he served as an intelligence officer, Kirk retired from the service in 2013 -- a year after he suffered a major stroke that still affects his mobility and speech today.