Surge, sag, repeat: Why the Republicans are so volatile.

"GOP voters: 'Can we see what it looks like with Huntsman and Perry again?' "

That satirical headline from The Onion just about sums it up: The 2012 Republican primary season has been like no other, and the idea that voters might want a second look at some of the dropouts – such as the former governor of Utah and current governor of Texas – isn't hopelessly far-fetched.

After all, after nine contests and tens of millions of dollars spent by the campaigns, 62 percent of Republican primary voters wish they had a bigger choice of candidates, up from 46 percent last fall, according to a New York Times/CBS News poll taken in mid-February.

Establishment favorite Mitt Romney just isn't closing the sale. And after a surprise sweep of the three Feb. 7 contests – Colorado, Minnesota, and Missouri – Rick Santorum has become the sixth Republican to surge in national polls, after Newt Gingrich, Herman Cain, Rick Perry, Michele Bachmann, and Donald Trump. Suddenly, polls show Mr. Romney, a Michigan native, in trouble heading into that state's primary on Feb. 28 – a race analysts say he has to win, or risk severe damage to his perceived inevitability as the nominee.

Why such a roller-coaster ride? Analysts point to several factors: a weak field of candidates; the advent of "super political-action committees," outside groups that can take in unlimited donations to fund advertising in support of a campaign; a Republican Party that is shifting rightward; and new party rules designed to extend the primary race.

In recent decades, Republicans have typically nominated the candidate who was "next in line" – usually someone who had run before. This year, that would be Romney. But the rise of the GOP's populist conservative base – centered in the tea party movement – has moved the goal posts rightward since he ran in 2008.

Romney, who governed Democratic-dominated Massachusetts as a moderate, is now viewed warily by conservatives. Never mind that he was positioned four years ago as the conservative alternative to John McCain, the eventual nominee. Since then, President Obama signed into law a sweeping health-care reform modeled on Romney's statewide reform. Romney has refused to disavow the Massachusetts law, but it's far from certain that it would help much if he did. A lot of conservatives just don't trust him.

Conservatives also look at history and see a formula for defeat.

"If you have an unenthusiastic base, you'll underperform," says Republican strategist Matt Mackowiak, who points to recent nominees on both sides who did not excite party activists and lost: Senator McCain and Robert Dole for Republicans; John Kerry and Michael Dukakis for Democrats. "They all had one thing in common – an unenthusiastic base."

Of course, there are plenty of base-pleasers who have lost. See George McGovern (D) and Barry Goldwater (R). And there have been establishment favorites who went on to win, starting with the two George Bushes. Many elements go into an electoral outcome.

But since the tea party burst onto the scene three years ago – an antiestablishment uprising over mortgage and bank bailouts that swiftly expanded – it might seem especially odd if the establishment candidate, Romney, winds up with the nomination. The problem for tea partyers is that they haven't coalesced around an alternative. Now, as former Speaker Gingrich fades, Mr. Santorum could be the one. (The other remaining candidate, the well-funded and organized Rep. Ron Paul of Texas, can be counted on to stay in the race and pull a decent number of votes, but his unorthodox foreign-policy positions prevent him from rising to the top.)

Santorum's viability could depend on his ability to withstand the onslaught of negative ads from both the Romney campaign and the biggest super PAC supporting Romney, Restore Our Future. It's the advent of these independently funded groups – greenlighted in 2010 by the Supreme Court ruling Citizens United v. Federal Election Commission – that has most jarred the old primary paradigm. 

Where once a candidate's reach was limited by his or her own fundraising, with relatively small individual donations, outside groups can now go wild with ad spending on a candidate's behalf, with just one well-heeled sugar daddy. Gingrich has casino magnate Sheldon Adelson. Santorum has investor Foster Friess.

"A lot of people thought [super PACs] helped Romney, but they've also helped Gingrich and Santorum stay in the race," says John Pitney, a political scientist at Claremont McKenna College in Claremont, Calif.

Both Gingrich's and Santorum's war chests have been modest, but their super PACs have allowed them to play in the big leagues, at least in terms of advertising. It was Adelson-funded ads slamming Romney's career at Bain Capital that helped Gingrich beat Romney in South Carolina. Now the Michigan showdown looms, and the Romney super PAC has pledged to spend at least $460,000 there.

In its first attack, Restore Our Future went up with an ad attacking Santorum, a former senator from Pennsylvania, as a “big spender” and a “Washington insider.” Anticipating an onslaught, Santorum launched his own ad lampooning Romney as “Rombo,” shooting mud at cardboard cutouts of Santorum.

The other key element extending the GOP race is the Republican National Committee's change of rules that requires proportional awarding of delegates in contests held before April. That has prevented the kind of early knockout punch that eliminated Romney four years ago.

"The RNC on purpose expanded the calendar to let other candidates emerge," says Saul Anuzis, RNC committeeman from Michigan. "We wanted the underdogs to have a chance."

But that extended process may be coming back to bite Romney, whom Mr. Anuzis backs. Romney, after all, started with all the advantages – high name recognition, a big fundraising and organizational network, and the experience of having run before. Now, with the new rules – and opposition super PACs – he's fighting for his political life.

Romney is also being forced to come to grips with an uncomfortable fact: A majority of Republican voters just haven't warmed up to him. While a series of "non-Romney" alternatives rise and fall around him, his national support has stayed remarkably even in the 25 to 35 percent range for months.

Republicans argue that an extended primary season will make the eventual nominee a better candidate. Their evidence: Mr. Obama waged an epic battle with Hillary Rodham Clinton for the 2008 Democratic nomination and went on to win the election.

So far in 2012, Romney's image has taken a hit. In mid-February, only 54 percent of Republicans viewed Romney favorably, versus 67 percent a month before, according to a CNN/ORC International poll. Among all Americans, only 34 percent had a favorable view of Romney, compared with 43 percent in January.

In contrast, Santorum's favorability among Republicans has gone up – from 49 percent in January to 56 percent in February. Among all Americans, Santorum's favorability has stayed essentially the same – 32 percent in February, 31 percent in January.

In 2008, Obama's image took a hit as he and then-Senator Clinton duked it out. But he recovered. So the question is whether the eventual GOP nominee can, too.

"That's an open question," says Dan Schnur, communications director of the McCain campaign in 2000. "If Romney can figure out a way to begin winning primaries by talking mainly about his own agenda and biography rather than by telling voters what's wrong with the other candidate, then this primary calendar will have worked to his benefit."

But, he adds, if Romney keeps winning primaries the way he won Florida – mainly via attack ads – then it will probably harm him going into November.

A debate in Mesa, Ariz., on Feb. 22 gives the candidates their next chance to frame their arguments before a national audience. Then comes the biggest cluster of primaries and caucuses of the cycle – not only the Michigan and Arizona primaries on Feb. 28, but also the 10 contests of Super Tuesday on March 6.

The biggest danger for the Republicans is that a dragged-out primary battle takes the party's image so far to the right that its nominee becomes unelectable, argues nonpartisan analyst Charlie Cook.

"That is the danger for Romney," writes Mr. Cook in National Journal, asserting that the former governor is still the likely nominee because of his money and organization. "He started out as a candidate very well positioned for a general election. Will he end up that way?"