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

Mitt Romney received 4,555,800 (58%) votes, beating Barack Obama who gained 3,294,440 (42%) by 1,261,360 votes in Texas.

Mitt Romney won 228 counties whereas Barack Obama won 26 counties in the total of the 254 counties in the State of Texas.

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 Texas, his 3,294,440 gained votes represent 5.0% of his popular vote victory. The remaining 49 states contributed to the remaining 95.0% 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 larger counties (Harris, Dallas, Tarrant), it is still possible for other candidates to catch up, given the amount of large counties that are there in the State of Texas.

Top 15 Counties Comparison in Primary Elections vs General Elections

General Elections
Barack Obama

General Elections
Mitt Romney

Harris, Dallas and Bexar, three of the larger counties, voted in favor of Barack Obama giving him a 133k vote advantage. Tarrant and Collin, some other larger counties, voted in favor of Mitt Romney giving him a 191k vote advantge. However, Mitt Romney's steady win in the less dense counties was enough to maintain that difference, making him gain an upper hand in the State of Texas.

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