The most perplexing question surrounding this year’s Republican race for the presidential nomination has been why can’t Mitt Romney seem to close the deal, despite running against what many consider an inferior set of opponents.

He has rarely exceeded 20 or 25 percent in national polls. And many pundits believe that the 25 percent support he has garnered thus far is about as far as Romney’s support will go — which leaves him extremely vulnerable to candidates like Newt Gingrich, who is working to distinguish himself as the latest ‘non-Romney’ candidate and consolidate much of the remaining 75 percent of the Republican vote.

There was Michelle Bachmann, Rick Perry, Herman Cain and now Gingrich. While the non-Romney’s rose and fell, Romney’s numbers have never seemed to move, with voters seemingly transferring their support from one surging candidate to the next.

“So far, with only three states having weighed in on who the nominee should be, I don't think it's fair to say that Romney isn't able to close the deal,” said Client Strategist for the Republican National Committee Eric Wilson. “At the end of the day, Republicans are going to unite around our nominee, because any of the candidates still in the race will make a better president than Barack Obama.”

If you look beyond the top-line data in the polls, it becomes clear that nowhere near 75 percent of Republican voters have been vehemently opposed to nominating Romney. A Gallup poll conducted before New Hampshire’s primary, for instance, found that only about 30 percent of Republican voters considered Romney an unacceptable nominee. These numbers have bounced around a bit from time to time and from survey to survey, but these results are fairly typical when questions like these are put to the voters.

About 25 percent of Republican voters are in Romney’s base (incidentally, about 22 percent of Republicans nationwide voted for Romney in their party’s primaries in 2008). And about 30 percent of the Republican primary electorate is truly opposed to him.

That leaves a swing group of about 45 percent of the vote. These voters can certainly imagine candidates that they’d prefer to Romney — but they also consider him an acceptable choice, more or less.

What seems to have become clear is that the hypothetical candidate these voters might have preferred to Romney has not materialized.

There are enough substantive and stylistic differences between the various non-Romney candidates that they should not be viewed as interchangeable, this evidence suggests. A considerable number of Santorum’s voters prefer Romney to Gingrich; a considerable number of Gingrich’s voters prefer Romney to Santorum.

And voters in the swing group are now settling for Romney. They are not necessarily doing so enthusiastically: A recent Pew poll found that there has been little improvement in Republican voters’ overall views of their candidates, which is unusual but not unprecedented.

The 2004 Democratic presidential race parallels this one in many ways.

For example, Democratic turnout was reasonably strong in November 2004, despite voters’ initial lack of enthusiasm for John Kerry. The opportunity to beat a polarizing incumbent is a powerful motivating force.

Jon Huntsman was candid when he offered insight into just how little faith Republicans have that Romney can beat Obama. Keep in mind, Huntsman has thrown his support behind Romney now that he is no longer in the race.

A recent Gallup poll found that GOP enthusiasm is on the decline. Republicans and Democrats are almost even, enthusiasm-wise, as they move further into the election year.

And the 2012 election is looking more like a carbon copy of 2008, which also looked an awful lot like 1996. Republicans are lining up behind Romney. The GOP seems to be coming to the realization that they have to nominate somebody, so it might as well be Mitt Romney.

But Romney's sudden downgrade from Republican frontrunner to potential also-ran coincided with a massive shift of conservative Christian voters in South Carolina to Gingrich's camp.

Why? Many observers trace it to lingering suspicion among evangelicals — a key Republican constituency — about Romney's Mormon faith.

And that has led some to suggest that Romney needs to make a speech about his Mormonism along the lines of John F. Kennedy's defense of his Catholicism to Protestant leaders during the 1960 campaign.

So could Romney pull a Kennedy? Should he?

Mike Huckabee, an evangelical favorite who sought the GOP nod in 2008, told Fox News after Romney's South Carolina implosion that the time had come for Romney to give it a shot.

"I do think he ought to address it," Huckabee said, arguing that such a speech would "sort of dismiss it, make it less important."Top of Form

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But few political observers, and apparently even fewer Romney's allies, appear to be urging that step.

For one thing, the tracking polls in the GOP contest over the past months have registered more spikes and dips than an erratic electrocardiogram. Romney's cardiac moment in South Carolina — and his continuing struggle heading into Tuesday’s Florida primary — needs to be seen in that context.

"I think it was more a result of Newt Gingrich catching fire combined with a pretty tough week for Mitt on issues like taxes and income," said David French, a social conservative and Romney ally who with his wife, Nancy, just published a book, "Why Evangelicals Should Support Mitt Romney (and Feel Good About It!)."

"It's a pretty conventional narrative — at least by the conventions of this very volatile race," French added. "If there was any blanket anti-Mormon sentiment, then Mitt would not have been up to begin with."

When Kennedy addressed the Greater Houston Ministerial Association in September 1960, it was only two months before the November election, and he did not have to worry about his Democratic base the way Romney has to worry about securing the GOP base to win the primaries.

Kennedy's chief task in 1960 actually was not to convert his audience; they were already a lost cause, and he knew it. What the Kennedy campaign hoped to do was to influence the 23 percent of the wider electorate who were still undecided.

"The campaign's polling showed that yes, if Kennedy could paint himself as a victim of anti-Catholic bigotry, that will move people your way," said Shaun Casey, a professor of Christian ethics at Wesley Theological Seminary and author of "The Making of a Catholic President: Kennedy vs. Nixon 1960." And it worked.

Romney's "religion" problem is about numbers as much as theology. As Casey notes, Kennedy's other task in Houston was to rally his Catholic base, which he did. But rallying an already strong GOP Mormon base wouldn't do much for Romney.

While Kennedy had a Catholic population of 40 million behind him — about one-quarter of the electorate, concentrated in key battleground states — Mormons today number just about 2 million, and are geographically concentrated in the Mountain West in mostly reliable red states (with the exception of toss-ups Nevada and Colorado).

Romney already gave a "Houston" speech — and it didn't work. Back in 2007, Romney was struggling to overcome evangelicals' doubts about his Mormon faith. While the speech was well received, it didn't move Iowa caucus-goers back then, and a second speech now would likely not convince suspicious evangelicals in Florida (and beyond).

Romney's biggest task is convincing conservative Christians that he is a conservative, not that he is a Christian.

Evangelicals have shown they are happy to back all sorts of unorthodox candidates – Herman Cain being a perfect example. Evangelicals may not love Mormons, but they are really down on moderates. Indeed, Romney is arguably "not Mormon enough," Richard Land, a top Southern Baptist official, said on the eve of the South Carolina vote.

"If his stance on life and his stance on marriage had been consistently what the stance of the Mormon church has been, he would have far less doubts among social conservatives," Land said.

Ralph Reed, head of the Faith and Freedom Coalition and a top evangelical political activist, said he doesn't think Romney's Mormonism will necessarily preclude him from winning evangelical votes or the GOP nomination, so he doesn't need to make the Kennedy speech at this point.

"Bottom line is," said Reed, "he may need to address it as the campaign proceeds, and he may choose to address it as part of a speech down the road."

In Florida, which is more diverse and less ideological than South Carolina, cooler heads could prevail if Romney can exploit his advantage in minions and millions. He has had the airwaves largely to himself for weeks, accompanied by a superior organization. Romney's campaign is in attack mode now – a sign that the campaign shares the Washington insiders' anxiety.

“The process is working and there's still time for voters to decide,” said Wilson. “Romney's greatest appeal continues to be the 'electability argument' and as long as he continues to raise the money needed to fuel his organization, he'll be in the contest. The other candidates remaining in the race don't have organizations on par with Romney so in many ways they're playing catch up.”

The New York Times Contributed to this report.

Zack Burgess is the enterprise writer for The Tribune. He is a freelance writer and Editor who covers culture, politics and sports. He can be contacted at zackburgess.com.