Take a guess who said this yesterday: “Voters are just now meeting the Real Romney — the buyout tycoon who executed takeovers, bankrupted businesses, and sent jobs overseas while killing American jobs.”

MoveOn.org? No, it was Rick Perry.

Let’s try another one: “Is capitalism really about the ability of a handful of rich people to manipulate the lives of thousands of other people and walk off with the money? I do draw a distinction between looting a company, leaving behind broken families and broken neighborhoods, and then leaving a factory that should be there.”

Bernie Sanders? No, it was Newt Gingrich.

Just over the last few days, Republicans targeting Mitt Romney have decided to go all in, going after the frontrunner’s career as a vulture capitalist — the guy who got rich orchestrating leveraged buyouts and laying off thousands of American workers. As John Dickerson noted, Romney’s GOP rivals are, whether they care to admit it or not, validating the larger Democratic line against Romney.

These attacks may help Romney’s primary challengers, and they will certainly soften up Mitt Romney for the general election. Importantly, they give credibility to an entire line of Democratic argument about income inequality and the destructive force of commerce. Before, Republican candidates could label those who would manage the excesses of the economy as socialists. The GOP critique of Romney ratifies the Democratic idea that the free market can breed excesses.

None of Romney’s rivals would admit they’re saying that, but when you pile on this completely and in such blunt terms you are embracing the anti-corporate energy that has always been behind the Democratic attack. When Barack Obama talks about the excesses of Wall Street, conservatives say he is punishing success. If so, then Romney’s rivals are doing the same thing.

Ed Kilgore had a similar item, noting that the GOP field is, in its quest to stop Romney, undermining “a central element of conservative ideology” and creating “a pretty good foundation for Democrats to build on.”

I’d take this just a bit further and ask a related question: why are so many Republican presidential candidates taking this line? Obviously because they think it’ll be effective, but do they believe that?

Romney has tried to argue that critics of his private-sector layoffs are borderline communists, trying to “put free enterprise on trial.” And yet, when there is no difference whatsoever between the message Dems are pushing and the attacks from Rick Perry, Newt Gingrich, and Jon Huntsman, it suggests the Romney line is a bust.

But more importantly, it also suggests the progressive line is what resonates with voters — even Republican voters. After all, it’s likely Perry, Gingrich, and Huntsman relied on polls and focus groups to identify the most potent message, and they all quickly found that this is the criticism that resonates.

For all the talk about this being a center-right nation, there’s a realization that Americans are uncomfortable with excessive greed and the kind of ruthless, screw-the-workers style of capitalism Romney used to get rich. If this discomfort didn’t exist, we wouldn’t see conservative Republican candidates using the argument to make appeals to conservative Republican voters.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.