A head to head comparison of the Missouri 2012 General Election gives us an idea of the break down of the voters.    

Mitt Romney received 1,478,960 (55%) votes, beating Barack Obama who gained 1,215,030 (45%) by 263,930 votes in Missouri.

Mitt Romney won 111 counties whereas Barack Obama won 4 counties in the total of the 115 counties in the State of Missouri.

Presidential General Elections

During the 2012 General elections, over 122M total number of votes were cast. Barack Obama got 62,614,654 (62.6 Million) over Mitt Romney's 59,141,654 (59.1 Million). He won the popular vote by 3,472,979 (3.4 Million). Even though he lost to Mitt Romney in the State of Missouri, his 1,215,030 gained votes represents 1.9% of his popular vote victory. The remaining 49 states contributed to the remaining 98.1% popular votes victory.

Top 15 Counties in Primary Elections vs General Elections

All Candidates (General Elections)

These 15 counties play an important role in these Primary elections. If a candidate, can get a sizable majority in the larger counties (St. Louis County, St. Charles, Jackson, St. Louis City), it becomes very difficult to win majorities in the smaller counties without voter outreach and increased voter participation in them.

Top 15 Counties Comparison in Primary Elections vs General Elections

General Elections
Barack Obama

General Elections
Mitt Romney

St. Louis County, Jackson and St. Louis City, three of the larger counties, voted in favor of Barack Obama giving him a 61k vote advantage. St. Charles, another larger county voted in favor of Mitt Romney giving him a 38k voter advantage in that county. However, Romney's steady win in the less dense counties was enough to overcome that deficit, making him gain an upper hand in the State of Missouri.

Related References: 2016 Missouri Primary Election Story, 2016 Missouri General Election Story, 2020 Missouri Primary Election Story, 2020 Missouri General Election Story