CORRECTION: An earlier version of this story misstated the sample size and margin of error of the Michigan poll. The poll surveyed 3,149 registered voters with a margin of error of plus-or-minus 1.8 percentage points.
Mitt Romney is locked in a neck-and-neck battle with Rick Santorum in next Tuesday's Michigan Republican presidential primary, but Romney holds a double-digit lead in Arizona, the other state to vote on Tuesday, according to an NBC News/Marist polls released early Wednesday.
Romney, who was born in the Wolverine State and whose father served as the state's governor in the 1960s, has a two-point lead over Santorum in Michigan, 37 percent to 35 percent, but the lead is statistically insignificant. Rep. Ron Paul, R-Texas, is at 13 percent in Michigan, with former House Speaker Newt Gingrich at 8 percent. Five percent are undecided or prefer another candidate.
In Arizona, however, Romney leads comfortably, outpacing Santorum, 43 percent to 27 percent. Gingrich is third in the Grand Canyon State, with 16 percent, followed by Paul at 11 percent. Just three percent of likely primary voters in Arizona are undecided.
That differs from a CNN/Time/ORC poll released late Tuesday that showed a much smaller lead for Romney, within that poll's margin of error.
Santorum manages to keep things close in Michigan by outperforming Romney among the most conservative voters. Among those who say they are "very conservative," Santorum leads Romney, 59 percent to 20 percent. Among tea party supporters, Santorum holds a 19-point advantage over the former Massachusetts governor.
Romney runs best among more moderate voters, and he also has a built-in advantage among those who have already voted: Those who said they voted absentee favor Romney, 49 percent to 26 percent.
Likely Republican primary voters say that Romney's favorite-son status is not affecting their vote, however. Just 10 percent say the fact that Romney was born and raised in the state makes them more likely to vote for him, while 88 percent say it makes no difference.
Romney's opposition to the federal government's rescue of the state's automobile industry during the Bush and Obama administrations is likely to result in a split decision, according to the poll. Half of Republican primary voters think "the bailout of the auto industry" was a bad idea, while 42 percent think it was a good idea. Despite Romney's opposition, his supporters are split nearly evenly on the question: 47 percent think it was a good idea, while 45 percent think it was a bad idea.
In Arizona, Romney's lead is much broader, as he captures sufficient support from more conservative voters. He trails Santorum by just two percentage points among tea party supporters, and he leads former Pennsylvania senator among voters who identify as "conservative" or "very conservative." As in other states, Romney runs best among more moderate voters, leading by 35 points among those who say they do not support the tea party.
Among early and absentee voters in Arizona, Romney has an even bigger lead, outpacing Santorum by 30 percentage points, 52 percent to 22 percent.
Both Michigan and Arizona are thought to be potential battleground states in the general election, though neither state was particularly competitive in 2008. But, among all registered voters, President Obama holds a commanding lead over Romney in Michigan, the poll shows, 51 percent to 33 percent. The race would be much closer in Arizona, where Romney leads Obama, 45 percent to 40 percent.
A 51-percent majority of voters in Michigan approve of the job Obama is doing as president, while 38 percent disapprove. In Arizona, those percentages are reversed: 38 percent of voters approve of Obama's job performance, and 51 percent disapprove.
The NBC News/Marist polls were conducted Feb. 19-20. In Michigan, the poll surveyed 3,149 registered voters and carries a margin of error of plus-or-minus 1.8 percentage points. There were 715 likely Republican primary voters; those results have a margin of error of plus-or-minus 3.7 percent.
In Arizona, 2,487 registered voters were surveyed, for a margin of error of plus-or-minus 2.0 percentage points. For the GOP primary, there were 767 likely primary voters, for a margin of error of plus-or-minus 3.5 percent.