Let us begin by stipulating that President Obama’s new budget plan is unrealistic, highly partisan and a non-starter on Capitol Hill.

That’s what’s so good about it.

At last, the president hasn’t conceded the race before the starter’s gun, hasn’t opened the bidding with his bottom line, hasn’t begun a game of strip poker in his boxer shorts. Whichever metaphor you choose, it was refreshing to see the president in the Rose Garden on Monday morning delivering a speech that, for once, appealed to the heart rather than the cerebrum.

“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,” the newly populist Obama declared.

Obama squinted into the morning sunlight and chopped the autumn air with his left hand. He got sputtering mad — literally — when he said his opponents would have us “settle for second-rate roads and second-rate bridges and second-rate airports and — and — and — schools that are crumbling.”

Then came that rarest of Obama moves: an ultimatum. “I will veto any bill that changes benefits for those who rely on Medicare but does not raise serious revenues by asking the wealthiest Americans or biggest corporations to pay their fair share.”

Republican howls of complaints began even before the speech.

Class warfare,” protested Paul Ryan.

Class warfare,” complained Karl Rove’s American Crossroads.

Class warfare,” judged House Speaker John Boehner.

The president welcomed the charge. “I reject the idea that asking a hedge fund manager to pay the same tax rate as a plumber or teacher is class warfare,” he told the Rose Garden crowd of 200. “I think it’s just the right thing to do.”

A moment later, the class warrior added: “Either we ask the wealthiest Americans to pay their fair share in taxes, or we’re going to have to ask seniors to pay more for Medicare. . . . Either we gut education and medical research, or we’ve got to reform the tax code so that the most profitable corporations have to give up tax loopholes that other companies don’t get. We can’t afford to do both. This is not class warfare. It’s math.”

The audience — a quickly assembled collection of students, retirees and federal bureaucrats — chuckled at this line. Obama didn’t crack a smile.

Whether his plan to tax the wealthy ever could — or should — become law is not really the point. Obama finally gave his side something to stand for after too much uncertainty. He also showed that he is finally learning to negotiate.

Had he called for a single-payer health-care system, he might have been able to win Republican support for the reform that was actually enacted. Had he held his ground earlier on tax increases for millionaires, he might have won more concessions from the GOP in the debt fights of the past year.

This late-term rally may be too late to save Obama, but it’s a welcome change. “The president made a very, very serious effort to reach agreement on a broad range of issues,” White House budget director Jack Lew told reporters after the Rose Garden speech. “When it became clear that there was no willingness on the other side to embrace a balanced approach with revenue, then we went back to put together a plan that reflects our view of how to do it.”

Monday’s Rose Garden revolution was televised — eight TV cameras faced Obama — but the president did not immediately adapt to his new role. Instead of pitchforks, there were teleprompters. Instead of revolutionaries, there were Tim Geithner and Jack Lew and Gene Sperling. Instead of launching into a Hugo Chavez stemwinder, Obama arrived 26 minutes late and began with a deficit discussion that put a woman in the second row to sleep.

Eventually, the president found his voice, describing Boehner’s refusal to consider tax increases. “The speaker says we can’t have it ‘my way or the highway,’ ” Obama said, “and then basically says my way — or the highway.”

He also challenged the opposition’s claim to represent the wishes of the Founders — quoting the first president on the necessity of taxes.

To that, he added one more bit of class struggle — “it’s not about numbers on a ledger,” but rather “about fairness” — before departing the Rose Garden.

Out on Pennsylvania Avenue, about 200 demonstrators in wheelchairs were rallying — in defense of Medicaid and in support of the millionaires tax. “No more cuts!” they chanted.

They don’t yet have the energy of the tea party, but, at long last, Obama has given his side a reason to fight.

More from PostOpinions

Milbank: Obama launches a revolution

Dionne: White House finally gets tough

Robinson: Obama’s tax plan is just common sense

Rubin: GOP can safely ignore Obama ‘vision’