McCaskill, considered among the most vulnerable of Democratic incumbent senators, capitalized on Akin's comments about pregnancy and rape to portray him as a right-wing extremist, and voters ultimately sided with her in a state increasingly favoring Republicans.
"It was very easy to vote against Akin with the things that he said," said Amanda Blinebry, a 27-year-old research specialist from St. Louis. "It wasn't hard to make that choice."
Akin apologized for his comments and admitted he was wrong, but top Republicans — Romney among them — called for him to drop out of the race. The six-term congressman refused, and even mounted a comeback late in his campaign.
According to a preliminary exit poll conducted in Missouri for The Associated Press, a solid majority of voters said they gave Akin's remark at least some consideration when they entered the voting booth, and those who did overwhelmingly sided with McCaskill.
Voters split nearly evenly between pro-choice and anti-abortion views, while exit polls showed that McCaskill performed well among women and Akin well among men.
"I like everything about him. He made one mistake. He apologized a dozen times," said 87-year-old John Shields, a resident of St. Louis County and the chairman of Schaeffer Manufacturing, in explaining his vote for Akin. "Every politician misspeaks and he misspoke on that issue."
Akin tried in vain to gloss over his "six-second mistake" and highlight McCaskill's close ties to Obama, including her support for his 2010 health care law and the 2009 stimulus act.
Nixon, seldom emphasizing his Democratic affiliation, became a two-term governor by pointing to his work in keeping the state's unemployment rate below the national average, and highlighting the addition of 17,900 jobs in August, when many undecided voters were weighing their choice.
Nixon also noted his steady leadership after natural disasters, including the deadly Joplin tornado and massive flooding along the Mississippi and Missouri rivers.
Spence, the former CEO of a St. Louis-based plastics company, was seeking his first elective office by arguing Missouri had fallen behind neighboring states in business development.
In other statewide races, Democratic Missouri House member Jason Kander defeated fellow state lawmaker Shane Schoeller early Wednesday to succeed Democratic Secretary of State Robin Carnahan, who opted not to run for a third term. Missouri Republican Lt. Gov. Peter Kinder secured a third term by defeating Democratic former state Auditor Susan Montee, and Missouri Attorney General Chris Koster won a second term by beating Ed martin, the chief of staff to a former Republican governor.
Democratic Treasurer Clint Zweifel also defeated Republican state Rep. Cole McNary.