I sketched out Romney's problem in an article, just published in Conscience, the excellent quarterly published by Catholics for Choice.  (You can read the whole thing, here.)  I talked this over with Rachel Tabachnick, who was raised as a conservative Southern Baptist, and knows the thinking of that world.  (She has since converted to Judaism and is a progressive Democrat.)  She believes that a lot of the kinds of Baptists she knew will not be able to vote for Romney.

She points to books and articles, currently available on the SBC's website for its LifeWay publishing empire and bookstore chain, suggesting that this mistrust of Mormonism remains unchanged for many. Indeed, a LifeWay Research poll of 1,000 American Protestant pastors last fall found that 75 percent of respondents did not consider Mormons to be Christians. Ed Stetzer, president of LifeWay Research, explained, "A person can respect a religious group and even appreciate their commitment to traditional moral values without equating their beliefs with Christian orthodoxy." They can, but whether they will is another question.

Tabachnick adds that Christian Right leaders know that they face an uphill
battle. She points to a recent edition of Rev. James Robison's television show, in
which he and Christian Nationalist advocate David Barton kept reminding viewers
that conservative broadcaster Glenn Beck is a Mormon, as if to help them find the
idea of Mormonism more acceptable. But even Beck may not be able assuage
the concerns of those schooled in conservative Baptist orthodoxy. Divisions on
the matter of Mormonism have been very public in recent years. In 2010,
Richard Land, the political point man in the SBC, stated that Mormonism is the
"fourth Abrahamic faith," and that he intended to work with Beck on a campaign
of national "renewal." But in a widely discussed commentary, Al Mohler's seminary colleague Russell Moore called this rapprochement with the Mormon faith a "scandal."
For his own part, Mohler tweeted Moore's commentary, as if to signal agreement.

A more organized effort was launched by You Tube evangelist, Jerry Johnson and some  fifty seminary professors, broadcasters, and pastors, mostly conservative Reformed Presbyterians of various sorts, called For the Sake of the Gospel. They argued that if conservative Christians are going to support Romney they should "clearly and unequivocally distancing yourself and Biblical Christianity from his Mormon beliefs."

They don't want there to be any uncertainty about whether "The Church of Jesus Christ of Latter-day Saints (Mormons), and historic evangelical Christianity are one and the same faith.  This we adamantly deny!"

Right Wing Watch reported in May that

Johnson explained, he personally will not be voting for either President Obama or Mitt Romney because that is like having to choose between "voting for the Beast or the False Prophet."

Of course, if there is some Christian activist out there urging Christian voters not to support Mitt Romney because of his Mormon faith, it is only a matter of time before they are invited to make their case on Steve Deace's radio program ... just as Johnson was last night.

Johnson made the case that Christians are misinformed about the true nature of Mormonism, thanks to people like David Barton who is "hugging and kissing all over Glenn Beck," and asked whether Christians would be willing to vote for a member of the First Church of Satan if the candidate supported the conservative agenda, warning that the "anybody but Obama" mindset was going to drive the nation and the church "into the arms of perdition" and prevent God from blessing America:

It appears that about six hundred people signed onto For the Sake of the Gospel's declaration, and the site does not seem to have been active since May. But this is probably the tip of one of many anti-Mormon icebergs.