Romney hasn’t been giving speeches about how Mormon theology is consonant with Trinitarian Christianity. Instead, he’s been dodging those kind of questions, while giving speeches arguing that his religious beliefs lead him to the same policy conclusions about abortion, same-sex marriage, and so forth, that conservative Catholics and evangelicals tend to reach. He’s arguing that his positions on the issues are more important than their theological underpinnings, in other words, not the other way around.
As the Byron York piece  on Romney related, the rare exception to this strategy of evasion took place when Romney thought he wasn’t being recorded and was being challenged very directly to embrace and display his religion. One of the things that has irritated some Mormons is Romney’s reluctance to speak about his religion, combined with his rare attempts to smooth over the differences (as he did when he was interviewed by Stephanopoulos), since it has given them (and others) the impression that he is somehow embarrassed or ashamed to speak publicly about it. He says that this is entirely untrue and is proud of his religion–just not so proud that he wants to tell you about it. When Romney evades these questions or his supporters make lame arguments about how we’re not choosing a “theologian-in-chief,” it declares to religious conservatives that he thinks that his religion is actually irrelevant to his “values.” In Romney’s case, this is not hard to believe, since he has been a lifelong Mormon and has only very recently discerned that his faith, into which others should not pry, authorises or inspires policy views that it had never inspired before. At that point, being a “person of faith” becomes rather more like a box that must be checked rather than being the core of the man.
As I have said more than once, one of Romney’s difficulties with religious conservatives is that he appeals to them thanks to the logic Ross mentioned (values, not theology) when I assume that many religious conservatives think that it matters how you obtain and arrive at those “values” and how you ground them in your religious teachings. This may not take precedence over everything, but the assumption Romney is making is that it doesn’t matter how he has arrived at sharing the same “values,” so long as he shares them. Yet what made George Bush such a favourite of evangelicals is that they could identify with how he had arrived at his beliefs and his conclusions. Perhaps this is an idiosyncratic objection on my part, but few things annoy me more than when people try to reduce witnessing a living faith and acting as leaven in the world to an adherence to a set of “values” and when they then give precedence to those “values” over actual doctrinal truths. That is fundamentally what Romney’s candidacy represents, it seems antithetical to what religious conservatives claim to believe, and it is why I expect that his currently broad but shallow support will collapse.