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

Barack Obama received 528,801 (53%) votes, beating Mitt Romney who gained 462,422 (46%) by 66,379 votes in Nevada.

Mitt Romney won 15 counties whereas Barack Obama won 12 counties in the total of the 17 counties in the State of Nevada.

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). His victory in the State of Nevada (with 528,801 votes) represents 0.8% of his popular vote victory. The remaining 49 states contributed to the remaining 99.2% 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 (Clark, Washoe), 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 a marginal win the an entire State. (As in the case of Mitt Romney in the State of Nevada)

Top 15 Counties Comparison in Primary Elections vs General Elections

General Elections
Barack Obama

General Elections
Mitt Romney

Clark and Washoe, two of the larger counties, voted in favor of Barack Obama giving him a 106K vote advantage. However, steady marginal wins for Mitt Romney in all the other counties (like Douglas, Lyon and Carson City) were not enough for him to catch up, making Barack Obama gain an upper hand in the State of Nevada.

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