John McCain built up massive popularity among American voters with his populist opposition to swindlers, liars and thieves, whether in business, Congress, labor or the defense community. His take-no-prisoners attitude toward corruption and his willingness to battle it wherever it crops up has made him an icon among our political leaders.

But in 2008, that John McCain has been under wraps as he catered to the Republican electorate.

Only the Arizona senator’s opposition to terrorism — to be sure, a real part of his agenda — was on display. His populism was anesthetized under a blanket of conformity and positive boosterism.

After he won the nomination, it seemed that he would continue fighting the Republican primaries forever. Bowing to the dictate to make peace with the fiscal conservatives who opposed him, he kept his sword sheathed and his mouth shut.

But this week, the old John McCain began to re-emerge. Articulating what tens of millions of Americans feel, he blamed the “greedy” of Wall Street for causing the current economic problems. He noted that it was their insatiable desire to get rich quick that led to the sub-prime frenzy that undermined sound economic growth and created a speculative bubble that had to burst. And he said that, as always, it is the little guy who will pay the price when a recession hits, while the greedy who caused it make out, well, like bandits.

This is precisely the kind of populist rhetoric that John McCain needs to embrace to have a chance to win the general election. He has got to draw a sharp distinction between himself and the stewards of Wall Street and side with Main Street in their battle against easy wealth and special privilege. By flanking the Democrats on the front of economic and social populism, McCain can be himself and can win.

Obama is making the social populist case against himself stronger with each passing day. His condemnation of small-town America and his elitist dismissal of religion, anti-immigration concerns and hunting as evidence of bitterness and the need for easy solutions was awful. Obama is, of course, right that trade protectionism and racial discrimination do, indeed, have their roots in bitterness and the need to scapegoat others for one’s own problems and shortcomings. But religion, concerns about immigration, and the sports of hunting and fishing hardly belong in the same category.

Through his own words, and those of his good reverend, Obama is painting himself into an Ivy League ghetto reminiscent of that which kept Mike Dukakis imprisoned for the campaign.

But it is up to McCain to carry the torch of economic populism. He should castigate those who are pocketing their winnings earned by inducing the poor to risk all on mortgages they couldn’t afford even as their unscrupulous practices have led the country to the brink of recession. He needs to take aim at credit card companies and student loan providers who are burdening our young families with debts that make it impossible for them to realize their dreams or to be the consumers we need them to be. He should go after the loose ethics of Congress, earmarking, and the plethora of abuses in our nation’s capital. He needs to resume his role as the leading opponent of Big Tobacco in Congress, warning about its tactics in luring millions of kids into lifetime addictions. He must demand that hedge fund entrepreneurs and other partnerships pay the same taxes as working people and end their special tax benefits.

Populism is neither left nor right. As a populist, McCain will bond with the average American opposing the elites that dominate the Democratic Party.

The real fissure in the Republican Party is not between centrists and conservatives. It is between the rich and the rest. The country-club Republicans, perpetually defending privilege, are out of sync with the American people. But McCain has always been in step with our priorities and it is refreshing to see him emerge anew onto the field of political battle. This John McCain, the populist defender of people against privilege, can win in 2008. The ever-so-cautious, watch-out-who-you-alienate Republican who won the primaries can’t.