Last week, Politico had an article that missed the point of the constitution. It begins with the statistic that 1 in 5 voters would be less likely to vote for a candidate who is Mormon. They then ask, "Doesn’t the Constitution say, in Article VI, 'No religious test shall ever be required as a qualification to any office or public trust under the United States?'"
They miss the point. The article is referring to a legal test. Nobody can be excluded from running for president on the grounds of his or her religion or lack thereof. The article says nothing abut an individual's right to vote for whomever they want for any reason that is important to them. If I want to vote for someone just because they practice one religious tradition or against someone because they practice another, that is my right.
They also misunderstand religion. If an individual truly believes a given religion, we can expect that it will impact the way that individual would see and experience the world which must impact the way they govern. If I knew that someone running for president was a young earth, 6 day creationist Christian, I wouldn't need to know anything else to vote against them. That would tell me a great deal about the way they would approach education policies, scientific research, and likely even foreign policy. A religious system, if truly embraced, must impact the way a person sees and acts in the world. Therefore, it is fair game for an individual voter to consider. Likewise, it tells me something if an individual claims to hold a faith but also says it will not impact the decisions they make. Then I wonder what does inform that person's decision making.
Of course, in the United States the question of religion is always more complicated. Some years back, Martin Marty referred to the "baptistification of America" - the idea that each individual can construct his or her own faith system and that no outside authority can impose itself on the individual (or local congregation). That means that one can no longer assume that a Catholic agrees with what the hierarchy of the Roman Catholic Church says even though that system clearly expects individual believers to follow the teachings of the Church. In the US, just because an individual is a Mormon does not necessarily mean that they abide by the directives of the Mormon church. While this trend cannot be ignored, we still can expect that any given religious system will have an impact on the particular paradigms in which a person lives.
The bottom line though is that one can vote for a candidate for any reason the individual feels is important - the color of their hair, their educational background, where they grew up, or their religion.