At the core of their concern is the atmosphere of daily vituperation among the top candidates. Mitt Romney, Rick Santorum and Newt Gingrich are now engaged in a seemingly constant knife fight, interrupted by only the sparest of positive, policy-oriented debate.

Worst of all, there is no clear end in sight for what has become, in the eyes of many Republicans, a joyless and prolonged nomination fight. Even Romney victories in Michigan and Arizona, the two states voting Tuesday, have little chance of forcing his aggrieved opponents out of the race. With a vast personal fortune at his disposal, there’s no prospect of Romney being shunted aside by his foes.

Haley Barbour, the former Mississippi governor and Republican Governors Association chairman, warned in a CBS interview Monday that the savagery of the campaign carries risks for Republicans and has “taken [attention] away from Obama’s policies.”

“Every day that any of the Republican candidates aren’t talking about the economics of this country is a challenge, because that’s how they’re going to win,” said Wisconsin Gov. Scott Walker, who told POLITICO there’s been “disproportionate attention” on personal clashes among the candidates.

Negativity in a presidential primary is nothing new: The 2008 Democratic nomination fight was no walk in the park and the 2000 race between George W. Bush and John McCain had moments of extreme nastiness.

But with the extended debate season and a massive influx of outside spending, along with a race that has lacked a dominant front-runner capable of wrapping up the nomination, the ugliness has lasted longer and has grown ever more personal. What’s more, unlike 2000 and 2008, there’s an incumbent president with no primary of his own, who stands to benefit from his opponents’ campaign of attrition.

“In terms of sustained negativity, there’s nothing like it in history,” said former Pennsylvania Gov. Ed Rendell, a top Hillary Clinton supporter in 2008.

Republican luminaries have begun to complain loudly, even while Romney battered Santorum on Monday as a Washington insider, Santorum assailed Romney as a phony conservative and Gingrich blasted Santorum for not being tough enough on unions.

Maine Gov. Paul LePage warned at the National Governors Association meeting in Washington over the weekend that the GOP primary had been “too messy” for any of the candidates to enter the fall campaign on a strong footing and urged his party to pick a “fresh face” at the Tampa convention this summer.

“‘I think the candidates, in my mind, have injured themselves and injured the party by not following Ronald Reagan’s ‘never speak badly of another Republican,’’’ LePage said. “They beat themselves up so badly that I’d think it’d be nice to have a fresh face.”

Even Virginia Gov. Bob McDonnell, a top Romney surrogate and potential running mate, said he wishes the campaign were “more positive,” though he argued that the GOP skirmishing was no worse than Democrats saw from their candidates in 2008.

That year, Barack Obama and Hillary Clinton clashed throughout the spring in their duel for delegates. But that race is still far short of the current campaign’s total-war atmosphere. Most of the punches were thrown in 2008 via surrogates — not the constant, direct sparring happening now.

One of the toughest 2008 ads questioned whether Obama was ready to take the “3 a.m. phone call” and respond to a national security emergency. The commercial caused an uproar but didn’t come close to the spots aired in 2012 that have pinned Gingrich with responsibility for China’s one-child policy and blamed Romney for single-handedly destroying towns in South Carolina.

“I think this is qualitatively different than our race,” said senior Obama adviser David Axelrod, who contended that the 2008 campaign focused on issues, with the candidates “conveying a sense of advocacy.”

“It’s a much different race than the one we had,” Axelrod added. “They spent a lot of time talking about the problems and challenges facing people in the country and less time talking about each other.”

In many cases, the 2012 culprits are Super PACs — the independent groups that have deployed huge sums of money to air attack ads without accountability. These have been the instruments for the most brutal television ads attacking Gingrich’s and Santorum’s voting records, and Romney’s background in private equity.

But the candidates have been more than happy to swing the ax themselves. It was Romney, not his super PAC, who labeled Gingrich an “influence peddler” on the debate stage and charged that Santorum had a record of betraying “the people.” It was Gingrich, not his super PAC, who accused Romney of trying to deny elderly Jews access to kosher food. When Romney said — in an obvious verbal screw-up — that he didn’t care about poor people, both Gingrich and Santorum hastened to call him heartless.

Democrats deeply engaged in the 2008 fight say their internal struggle couldn’t measure up to the GOP campaign. A better analogy, several said, might be the 2000 primary between Bush and McCain, which legendarily featured shady phone calls in South Carolina telling voters McCain had fathered a child out of wedlock.

One Republican involved in that cycle said 2012 was actually “a bit nastier.” Said another: “It’s tougher between the candidates [this time.]” And however nasty it was, 2000 was also a shorter race than the 2012 campaign, which promises weeks or months of endless, unrestricted hostility.

“There was very little of this in tone or substance with Hillary and Barack. That campaign was basically substantive issues. There were disputes about experience — whether Hillary was too tied to the establishment, whether Barack had enough experience,” Rendell said. “The Clinton-Obama primary made Barack a stronger candidate, whereas I think this will make whoever emerges inherently a weaker candidate.”

Added Rendell: “In terms of reelecting the president and bringing back a Democratic Congress, I’m delighted. … In terms of taking the longer view and the effect on American democracy, in many ways it’s heartbreaking.”

Center for American Progress head Neera Tanden, who has advised both Clinton and Obama, agreed that “it’s like people were using knives in 2008 and these guys are using nuclear bombs.”

That’s not to say, she said, that things in 2008 didn’t get personal — just not this personal.

“It was a character contrast. [Obama’s] overall point was that Hillary was dishonest, but he never went into a debate and said, ‘You’re a liar.’ Everything was subtle,” she said. “It was all allusion. The criticism was based on character … but it was like night and day.”

To Republicans inside the 2012 campaign, the Democrats’ version of events is too cute by half. It’s easy in retrospect, they say, to downplay the angst of top Democrats at a long primary pitting two historic, well-funded candidates with passionate bases of support against one another.

Even if the 2008 candidates didn’t directly accuse one another of racism and sexism, there was a toxic element to the nomination fight that’s absent in this campaign, Republicans say.

“Hard to see that the [2012 is uglier] when the last primary had such undercurrents of race and such bitterness. Until a former president starts crying and sputtering that he isn’t a racist, I think the Dems have this one beat,” Romney adviser Stuart Stevens wrote in an email.

The Republican race, Stevens argued, is “more issue focused and less destructive” than the 2008 primaries, despite what Democrats may recall.

“Look at what the Obama campaign said about Hillary — she has no core, she will say anything, etc. I think it is hard to find a more nasty, brutish campaign,” Stevens wrote.

The “no core” line is one that the Obama camp has used more recently — against Romney, quite frequently, in the 2012 race.

Santorum adviser John Brabender had a different take on the negativity of the 2012 race, pinning blame squarely on the Romney camp and its repeated efforts to tear down conservative challengers.

“Look, I agree there’s a lot of fights going on. … You had Romney versus [Rick] Perry, then Romney versus Gingrich, then Romney versus Santorum,” Brabender said. “Romney has unleashed this nuclear attack on candidate after candidate and the other candidates are in a position where they’re not going to sit back and take it.”

Whether or not the 2012 primaries are literally the most negative in memory, there’s no question that the race is taking a uniquely painful toll on the Republican field.

While the 2008 primaries were certainly divisive for a time, none of the candidates received the severe, lasting damage that surveys show for the 2012 field. The POLITICO/George Washington University Battleground Poll published Monday placed three Republican candidates — Romney, Gingrich and Ron Paul — in horrendously negative territory among voters, with Santorum well on his way in the same direction.

Republican pollsters Ed Goeas and Brian Nienaber, who conducted the poll with the Democratic firm Lake Research, wrote in an analysis that their party’s candidates were essentially eating themselves alive.

“Rick Santorum, who is essentially the new kid on the block, has a favorable image with a plurality of the electorate (39% favorable to 36% unfavorable), but the other three Republican candidates are ‘upside down’ with their unfavorable image exceeding their favorable image with the overall electorate,” they wrote. “The candidates who have been in the national spotlight longer — Gingrich (26% favorable to 62% unfavorable) and Romney (38% favorable to 51% unfavorable) — have actually reached a majority unfavorable rating while Ron Paul (30% favorable to 46% unfavorable) holds a plurality unfavorable rating.”

The pollsters continued: “The bottom line being, this is a trend that must be reversed before the general election if Republicans expect to be truly competitive in the fall.”

Former Clinton adviser Paul Begala said that at this point, the 2012 primaries have gotten “dirty” in a way the 2008 race never did.

“It’s getting very personal,” Begala said: “When Newt Gingrich is calling Gov. Romney a despicable liar — as opposed to the charming liars, I guess — … the governor is attacking Santorum today for being a lobbyist for the World Wrestling [Federation.] They’re using attacks that are a little too much for us.”

That — combined with a sense that the party is still too negative in its general-election messaging — is prompting more and more GOP officials to wax gloomy.

“There’s just such a toxic atmosphere right now, specifically in the Republican Party. And I would love to say that it’s gonna be all about ideas and solutions,” former Arkansas Gov. Mike Huckabee said in an interview on Israeli television. “Unfortunately, a lot of it is about just being able to say, I’m more angry at the Obama administration than somebody else.”

Jonathan Martin, James Hohmann, Glenn Thrush and David Catanese contributed to this report.