In our us-versus-them culture, every political campaign is a battle to define who exactly the "us" and "them" are. Republicans typically say it is natives versus immigrants, Christians versus non-Christians and heartland folks versus Hollywood elites. At their most effective, Democrats parry by defining the "us" as the majority of working people, and the "them" as the tiny group of plutocrats who control the country.

In recent years, Democrats have stopped making this case for fear of offending their big donors. But this is exactly the argument they must make if they hope to defeat John McCain.

With Barack Obama on the ticket and primary exit polls showing many considering race in their vote, the GOP's traditional black-versus-white attacks are sure to be just as overt as they were during the party's halcyon days employing "welfare queen" and Willie Horton imagery — only this time, they'll use Internet rumors to imply that Obama is a Manchurian candidate. McCain's first ad, in fact, trumpets the Arizona senator as an "American president" — not-so-subtly crafted to imply that the multiethnic Obama is un-American.

The way for Obama to counter this racial onslaught is through class-based politics — and what a golden opportunity McCain presents for that on the issue of trade.

Despite its five letters, NAFTA is American politics' most offensive four-letter word. The lobbyist-written pact symbolizes globalization policies that force Americans into a wage-slashing, environment-destroying, union-busting competition with foreign workers.

NAFTA-style trade policies are now so unpopular that a recent Wall Street Journal poll found 60 percent of Republicans oppose them. And yet, McCain continues to stage public events supporting NAFTA.

McCain's position is backed by an Establishment media that justifies "free" trade orthodoxy with the kind of fact-free platitudes that marked New York Times contributor Roger Lowenstein's trade write-up this week. He told readers that in driving down prices for goods, free trade helps workers. Left unsaid is the fact that, in the NAFTA era, wages have not kept pace with inflation. So while prices may be driven down somewhat by forcing domestic workers into competition with foreign slave labor, wages are dropping faster than prices, meaning Americans are losing out in the deal.

Pointing out this data and promoting a new, fairer trade agenda is Obama's clearest way to the presidency.

Substantively, he can argue that America should return to fair trade and strategic protections — the kinds of policies that originally built our economy into a powerhouse. Politically, he can hammer McCain for championing a trade policy that has economically destroyed key swing states from Maine to Ohio — and polling suggests populist positions on trade may be precisely what swings general election voters. According to a Democracy Corps survey, Republicans who considered voting Democratic in 2006 were most put off by the GOP's support for job-killing trade agreements, meaning Obama could swing these if he champions a fair trade agenda.

That's a big if.

For every loud speech Obama has given about making sure trade pacts "are good not just for Wall Street, but also for Main Street," he has made a quiet move reassuring Wall Street that Main Street will be ignored. Last week, for example, he named Jason Furman as his top economic adviser. Furman has spent the last few years defending Wal-Mart and working closely with Bob Rubin, the Citigroup chairman who championed NAFTA as Bill Clinton's Treasury secretary.

In the battle to define us-versus-them, Obama hasn't yet made a convincing case that he stands with "us" on economic issues. But if he does and he counters the inevitable race baiting with a class-unifying message, he will win the White House and — more importantly — start the long process of rebuilding America.

David Sirota is a bestselling author whose newest book, "The Uprising," was just released in June of 2008. He is a fellow at the Campaign for America's Future and a board member of the Progressive States Network — both nonpartisan organizations. His blog is at www.credoaction.com/sirota.

COPYRIGHT 2008 CREATORS SYNDICATE, INC.