(CNN) As an anti-war activist in the early 2000s, Arizona Senate candidate Kyrsten Sinema led a group that distributed flyers depicting an American soldier as a skeleton inflicting "U.S. terror" in Iraq and the Middle East.

The flyers could become an issue for Sinema, the Democratic nominee challenging Republican Martha McSally in one of the most competitive US Senate races this year. CNN rates the race as a toss-up.

Currently one of only 18 members of the Blue Dog Coalition in Congress, a caucus of centrist and conservative Democrats that once boasted 54 members, Sinema's time organizing anti-war rallies highlights how her views have shifted since the early 2000s, when she ran for state and local office as an independent affiliated with the Green Party and was viewed as one of the most progressive activists in Arizona.

"Kyrsten comes from a military family and is very proud of her record supporting Arizona's servicemembers, veterans, and their families," Sinema campaign spokeswoman Helen Hare said in an emailed comment to CNN's KFile. "Attacks on Kyrsten's respect for those who serve have already been called out as false, and Kyrsten is going to stay focused on the issues that matter most to Arizonans -- like making sure Congresswoman McSally and her allies can't roll back protections for patients with pre-existing conditions."

Hare added that Sinema did not approve or design the flyers at the time. The campaign further noted that two of her brothers have served in the military and that one remains on active duty in the Navy.