The former's record on immigration is firmly established. He led the Republican charge against Proposition 200 in 2004, which was ultimately approved of and passed by 56%-44% of Arizonans. He put forward the McCain-Kennedy amnesty bill. Americans for Better Immigration (run by NumbersUSA), which grades all members of Congress based on their immigration-related voting records, gives him a 'D'.
Mitt Romney is more of a question mark. His past Congressional donations do not reveal a pattern regarding their respective stances on immigration, although on net they've gone to those who are slightly more restrictive than Congress as a whole. He did little one way or another regarding illegal immigration while Governor of Massachusetts. On the campaign trail, Romney's gone after Giuliani for NYC's status as a sanctuary city under his mayorship, and he's criticized McCain for the aforementioned amnesty bill.
It's evident, at least in the blogosphere, many of those who plan to vote on the Republican side during the primaries are not particularly impressed by either candidate.
What about our elected leaders? With apologies to Machiavelli, perhaps the first method for measuring a man on the sincerity of his positions on immigration is to look at the legislative men he has behind him. Thus far, Romney has received 42 Congressional endorsements. There have been 36 for McCain.
Using AfBI's gradecard scoring system, I tracked the performance of those 78 congress critters. Regarding the way AfBI makes the grade calculations, in an attempt to remain as objective as possible, they are based on immigration reduction rather than looking at the nuances in legislation dealing with illegal immigration. They treat H-2A and H-1B visas in an equally negative light. If you see unskilled immigration from Latin America as disastrous but favor some sort of limited merit immigration system for the cream of the world's crop, it may not be optimal. But as the most comprehensive measure available, it is useful.
ROMNEY'S BACKERS HAVE A RESTRICTIONIST GPA OF 3.4 TO THE MCCAIN CROWD'S 2.4. That's substantial. Of course, these endorsements are influenced by a whole host of considerations, of which Romney's perceived alignment with their legislative agenda on immigration is just one. But Romney does better than the GOP as a whole, while McCain performs even worse than the slate of Republicans who were thrown out in the '06 midterms--and that was a group of relatively open-borders Republicans--not to mention the party as a whole.
John Savage suggests that Mormonism tends to encourage a universalist one-worlder view. The implication is that Romney might, like McCain and Huckabee (only Ron Paul has been consistent in his opposition to things like the Visa Lottery system and the anchor-baby interpretation of the 14th Amendment), want to keep the flood gates open even though he's said otherwise during the campaign.
It's possible, but I don't see much indication that it is probable. Romney doesn't appear to wear his religion on his sleeve (although he does not smoke or drink), and it's hard to determine much about an individual based on the average tendencies of the demographic group he belongs to. In his 2004 book, Mormonism is apparently not a focal point (in making this assumption I'm going off of Amazon reader reviews--I've not read the book myself).
While Mormonism, like the gamut of Protestant denominations and Catholicism, is ecumenical by nature, Judaism is not. Yet Jews are consistently less restrictionist than Protestants or Catholics. A comprehensive Zogby survey found self-described 'born again' Christians to be the most strongly in favor of reducing immigration levels among the major religious classifications considered.
The circumstantial evidence points to Romney as a better choice than McCain for Republican primary voters concerned about immigration into the US.
