FiveThirtyEight.com's Nate Silver breaks down the support in Arizona for Romney and finds that Mormon voters were a huge advantage for him.
Mormons made up nearly one out of every seven voters in Arizona’s primary. Mr. Romney carried 9 in 10 of these Mormon votes.
But this advantage among Mormons also appeared to produce some other unusual voting patterns. For example, while Mr. Paul had been consistently winning younger voters, in Arizona Mr. Romney won twice as many votes among those 18 to 29. This reason becomes more clear when one considers that Mormon voters are considerably younger than the typical Arizona voter. While only 1 in 10 Arizona voters overall were between 18 to 29, among Mormons nearly 4 in 10 fell into this age category.
Similarly, while in other states Mr. Romney had generally been losing among voters who said abortion should be illegal in all cases, in Arizona he drew almost as much support as Rick Santorum (about 2 in 5 of these voters). However, if Mormon voters are excluded, Mr. Romney only wins half as many anti-abortion votes as Mr. Santorum.