Bernie Sanders is on his way to folk hero status around the nation because of his ardent opposition to tax breaks for the wealthy.

His eight-and-a-half-hour speech last Friday was the sort of dramatic gesture that captures the imagination. He spoke words that many Democrats were hoping to hear from President Obama.

Instead, Obama’s compromise with the Republican Senate leadership is moving toward passage by Congress, without the support of Sanders and other liberals, including Rep. Peter Welch and Sen. Patrick Leahy.

Sanders’s attack on the tax deal was embedded in a critique of the economic inequities resulting from the class warfare waged by the wealthy against the nation over several decades. He detailed the extent to which the wealth of the nation has become concentrated among the wealthiest few. And he warned that continuing Bush era tax cuts for the wealthy and cutting estate taxes as proposed in the Obama-McConnell compromise would only accelerate the upward transfer of wealth.

Sanders’s speech was not technically a filibuster, but the speech’s length served the purpose of drawing attention to Sanders’s case and cast him in a heroic role as a battler for the little guy.

It is the role that Sanders has assumed his entire life. What’s different now is that he has the stage of the U.S. Senate at his command and a moment in history when his views on economic justice and its lack have special resonance.

For Obama, Sanders is serving a useful role that might well have been anticipated by Obama’s political strategists. Sanders is giving definition and force to the position of the left, voicing a liberal critique with which Obama may agree in many ways. By energizing the left, Sanders and his allies are dragging the argument toward the left in the same way that, in recent years, extremists on the right have dragged the argument toward the right.

As president, Obama has the difficult job of cobbling together positions that will draw majority support. He cannot afford to tailor his appeal to the narrow spectrum of the left, even if the leftist critique has becoming increasingly apt.

It is no coincidence that President Clinton made an appearance at the White House last week to lend his support to the Obama compromise. As president, Clinton perfected the art of triangulation — forging a position somewhere between the extremes of left and right. Sanders has given Obama a point on the triangle from which he can triangulate.

As poster boy for the left, Sanders has now begun to generate murmurings of a Sanders-for-president movement in 2012. Sarah Palin, poster girl of the right, generates the same sort of talk. Neither is a realistic candidate, though each serves to demarcate the outward verge of their parties’ territory. And each can toy with the idea as a way to pull the candidates in their directions. So far Sanders has not shown any sign he wishes to indulge such a fantasy, even as a tactical gesture.

Sanders is a unique political character in Vermont and the nation. He calls himself a socialist in the vein of the early 20th century American socialist Eugene Debs and favors the kind of social welfare programs that are an ordinary part of life in the social democracies of western Europe.

Over the years he has been a consistent critic of the irresponsible profiteering and greed of American corporations — a view often ignored during those decades when the economy seemed to be prospering and companies were doing well.

But in the decade of the 2000s, Sanders’s warnings about the pillaging of the economy by reckless corporations proved prophetic. Sanders’s dire warnings turned out to be, not pronouncements of an ideologue, but descriptions of reality.

Obama still must deal with the Republicans in Congress and so has been forced to engage in the fancy footwork of compromise and triangulation. Sanders serves Obama well by strengthening the case of the left, creating a counterweight to the relentless forces amassed on the right to serve the interests of the wealthy and powerful.