|Christus statue replica commissioned by the Church of Jesus Christ of Latter-day Saints|
that grace LDS buildings around the world
A pastor's introduction of Rick Perry wherein Mitt Romney was described as not being a Christian on Friday has pundits attempting to stir up controversy among GOP presidential contenders.
The meta question is interesting, as it seems the media is trying to create controversy where there is little, in that no candidate is exhibiting overt bigotry nor are they (at least not to my knowledge) trying to do what Mike Huckabee did covertly in 2008 in undermining the Romney candidacy simply over the Mormon issue, bless his heart.
This makes some sense: these candidates have had multiple contacts with Latter-day Saints (lingo for members of The Church of Jesus Christ of Latter-day Saints, the official name of the church and what members call themselves; Mormon is a nickname that derives from the ancient prophet who compiled the Book of Mormon, a 1,000 year spiritual history of the "Christians"in the Americas) and, as is typical, better familiarity with Latter-day Saints (as is true for most sects) translates into less fear and ignorance-based bigotry. Although my limited interactions with some of the candidates can't count for much, I know this in part from personal knowledge.
Yet the question still goes begging: are Mormons Christians?
Not to be overly-legal, but it truly depends on how you define "Christian." An historical answer will define this via periodization.
The first Christians in Antioch were called such because they followed the teachings of Christ and had faith in His saving power. If you limit the definition of Christian to this time or period as Latter-day Saints do, Mormons are emphatically Christian.
Later doctrines were institutionalized with pagan Roman emperor Constantine's shepherding bickering religious clerics into congress to agree upon and adopt universal dogmas that could be recognized and systematized throughout the empire. The result was the Nicean Creed of 325, which identified the Trinity, or the bodily unity of Father, Son, and Holy Ghost (compared to the corporeal belief of Latter-day Saints), as established doctrine. If one dates the definition of "Christian" to this point in history, delimiting "Christian" as one who accepts the Nicean creed, one could say Mormons are not Christian.
Because the Latter-day Saint believes that a general apostasy occurred sometime after 100 AD but certainly before 300 AD, they do not accept the Nicean creed, and are the only Christ-believing sect (unless, of course, Jews for Jesus self-identifies as a sect) to do so.
To even write the phrase "Mormons are not Christian" produces a visceral reaction in me. My relationship with the Savior in part defines me. I aspire to base my life on His precepts and access the mercy of his Atonement wrought in the garden and on the cross on a daily basis. I attempt to live a Christ-centered life. Hearing (or writing) that I am not a Christian is to deny and defy this central part of my life.
Yet I know empirically that the definition varies based on belief systems that place the origins of Christianity in different periods. I date it to the time of Christ, not to Constantine.