An exit poll conducted for The Associated Press showed that Akin's "legitimate rape" remark was taken into consideration by many Missouri voters, and women were slightly more likely to say it was important to their decision.
Republican Dorothy Gilpin voted for Romney for president but switched parties to vote for McCaskill.
"I thought she was better than that Todd Akin. I didn't like his comment about getting raped," said Gilpin, a retiree from Jefferson City.
Akin's supporters were more likely to forgive his remark.
"He made one mistake. He apologized a dozen times. Every politician misspeaks," said John Shields, of St. Louis County, who is chairman of Schaeffer Manufacturing.
Akin eventually regained support from some Republicans — including former presidential candidates Newt Gingrich, Rick Santorum and Mike Huckabee — and got financial backing from several conservative interest groups, including a $1 million ad buy from the Now or Never Political Action Committee.
But McCaskill generally enjoyed a financial advantage throughout the campaign. She also highlighted Akin's opposition to the federal government's role in issuing student loans and setting a minimum wage.
Even before the Aug. 7 Republican primary, McCaskill seemed to prefer to run against Akin. She took the unusual step of running TV advertisements against her three potential Republican opponents. The ad about Akin highlighted positions appealing to Republican primary voters. It called Akin a "crusader against bigger government" who promotes a "pro-family agenda," and it ended with the claim that Akin "is just too conservative."
McCaskill, 59, has a lengthy political resume that includes serving as state auditor, a state lawmaker and a county prosecutor in the Kansas City area. She now lives in suburban St. Louis.
Akin, 65, is a former Army officer, engineer and state lawmaker. He first won election to the U.S. House in 2000.