This has to be the clearest sign yet that Obama has taken a very sharp populist turn as he seeks to frame the contrast between the parties heading into 2012. During his remarks this morning, Obama directly responded to Republicans accusing him of “class warfare,” but rather than simply deny the charge, he made the critical point that the act of protecting tax cuts for the rich is itself class warfare, in effect positioning himself as the defender of the middle class against GOP class warriors on behalf of the wealthy.

A senior administration official tells me that parts of Obama’s “class warfare” broadside were ad-libbed. Here’s the key chunk — and it’s a script that could have been written by just about any card-carrying member of the “professional left”:

Warren Buffett’s secretary shouldn’t pay a higher tax rate than Warren Buffett. There’s no justification for it. It is wrong that in the United States of America, a teacher or a nurse or a construction worker who earns $50,000 should pay higher tax rates than somebody pulling in $50 million...

We’re already hearing the usual defenders of these kinds of loopholes saying, “this is just class warfare.” I reject the idea that asking a hedge fund manager to pay the same tax rate as a plumber or a teacher is class warfare. I think it’s just the right thing to do. I believe the American middle class, who’ve been pressured relentlesly for decades, believe it’s time that they were fought for as hard as the lobbyists and some lawmakers have fought to protect special treatment for billionaires and big corporations.

Nobody wants to punish success in America ... All I’m saying is, that those who have done well, including me, should pay our fair share in taxes to contribute to the nation that made our success possible.

This is as clear a sign as you could want that the White House is trying a dramatically different approach this time than it has in the past. The White House knows that the GOP is all but certain to reject many of Obama’s deficit supercommittee proposals. But that’s precisely what makes the new approach significant.

During past standoffs the White House signaled early on in the process that it was prepared to give ground on core liberal priorities in the name of compromise. At the outset of the debt limit fight, for instance, Obama quickly signaled that he knew his initial insistence on a “clean”debt ceiling hike was a nonstarter for Republicans, and that as a result, he’d have to accede to the GOP demand for spending cuts in exchange for it. But this time, the fact that tax hikes are a non-starter for Republicans is dictating the opposite approach — he’s actively seeking a sustained confrontation over something Republicans are reflexively opposed to, in the belief that even if a compromise isn’t reached, it will amount to a political winner for the White House and Democrats.

Relatedly, there’s a ton of commentary out there today to the effect that this new posture is about nothing more than appealing to the Dem base. But that’s thoroughly bogus: Whether they’re right or wrong, Obama and his advisers have also decided that this is a good way to appeal to independents, too. Polling shows that while indys marginally disapprove of Obama’s jobs plan, and are deeply skeptical of his performance on the economy, solid majorities of them support his actual jobs-creation prescriptions. Obama advisers reportedly believe that the best way to win back independents is to be seen as a fighter for their behalf on jobs. That’s why Obama went out of his way to argue that the “American middle class” needs to be “fought for” as hard as GOP class warriors are fighting for “billionaires and big corporations.”

I don’t know how long he’ll sustain this fighting posture. And as Jamison Foser notes, the jury is still out on how the ultimate compromise Obama does agree to — if a compromise is reached — will impact lower income folks and Medicare recipients.

But for now, at least, this is a clear sign that the “professional left” — which has long argued that showing fight is far more important to independents than chasing after compromise for its own sake — is getting what it wants.

UPDATE: Despite widespread commentary to the contrary, this new approach is not just about winning back the Democratic base; it’s also about trying to win back independents.