A head to head comparison of the 2008 Missouri General Election gives us an idea of the break down of the voters.    

John McCain received 1,445,814 (49%) votes, beating Barack Obama who gained 1,441,911 (49%) by just 3,903 votes in Missouri.

John McCain won 107 counties whereas Barack Obama won 9 counties in the total of the 116 counties in the State of Missouri.

Presidential General Elections

During the 2008 General elections, over 131M total number of votes were cast. Barack Obama got 69,448,278 (69.4 Million) over John McCain's 61,739,059 (61.7 Million). He won the popular vote by 7,709,219 (7.7 Million). Even though he lost to John McCain in the State of Missouri, his 1,441,911 votes represents 2.0% of his popular vote victory. The remaining 49 states contributed to the remaining 98.0% 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 largest 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. However, steady win margins in less popular counties can amount the marginal win to win the entire State. (As in the case of John McCain in the State of Missouri).

Top 15 Counties Comparison in Primary Elections vs General Elections

General Elections
Barack Obama

General Elections
John McCain

St. Louis County and St. Louis City, two of the larger counties, voted in favor of Barack Obama giving him a 219k vote advantage. St. Charles and Jackson, another larger counties, voted in favor of John McCain giving him a 20k vote advantage. However, John McCain's steady marginal wins in the less popular counties were just 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, 2012 Missouri General Election Story