One of the central tenets of modern Republican thought is the assumption that the United States is a center-right nation. Americans are rugged individualists who reflexively distrust government, are offended by “welfare,” and believe social programs do more harm than good. It’s why, the theory goes, candidates can never go wrong offering more tax cuts and less spending.

Of course, these center-right assumptions tend to be pretty dubious in practice. Americans often see government playing a constructive role in society, and have come to appreciate and rely on many bedrock social programs (Social Security, public schools, Medicare, law enforcement, etc.).

At a certain level, even a radicalized Republican Party recognizes the limits of these center-right assumptions. Greg Sargent, for example, flags a new GOP attack ad going after a Democrat from the left, accusing him of failing to honor the “social safety net.”

…Republicans have again taken to attacking Dems from the left on Medicare after doing it successfully last cycle, arguing that Democrats are the only ones who have ever voted to cut the program and insisting that Dems are intent on destroying Medicare by doing nothing to save it.

Here is the most amazing example of this yet — a remarkable new ad from the [National Republican Congressional Committee] that accuses Dem Rep. Jerry Costello of Illinois of supporting a “Democrat plan” that would “decimate” Medicare, “shred the social safety net,” and “leave seniors at risk.”

The substance, such as it is, behind the ad is so blisteringly stupid, I’m almost inclined to give the NRCC credit for its creativity. As the pitch goes, Costello opposed the radical Republican plan to end Medicare. That means, the NRCC says, Costello wants to leave Medicare alone. And that means, because Medicare faces long-term financing challenges, Costello’s alleged approach would eventually lead to Medicare cuts that would “shred the social safety net.”

Orwell would be proud. Those trying to shred the social safety net are accusing those trying to protect the social safety net of wanting to shred the social safety net. Wow.

But in the larger context, Greg added, “[T]he fact that Republicans are now attacking Democrats from the left on Medicare amounts to an acknowledgment that Dems have won the debate over Ryancare.”

Agreed. Once the discussion boils down to which party loves Medicare and wants to protect the safety net more, the game is no longer being played by Republican rules. Indeed, the moment the National Republican Congressional Committee is going after a Democrat from the left — someone has to protect the safety net from those callous Democrats — the whole notion of a center-right nation starts to look pretty silly.

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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.