By Jonathan Allen, CQ Staff

If there is a sleeper issue with the potential to catapult Barack Obama past Hillary Rodham Clinton in the remaining delegate-rich Rust Belt states, it is the North American Free Trade Agreement, according to political experts.

Many of the working-class white Democrats who form a pillar of Clinton’s base blame the pact and trade agreements like it for the migration of the American manufacturing base to other countries. And it was her husband, Bill Clinton, who pushed it through Congress during his first term in the White House.

“I don’t think there’s any doubt that NAFTA is incredibly unpopular with a base of voters that Sen. Clinton really needs,” said Jon Delano, a political scientist at Carnegie Mellon University in Pittsburgh. “What she needs to do is move beyond it and stress what she would do to correct the situation now. That will resonate, whether it comes from her or Sen. Obama.”

Exit polls in Tuesday’s Wisconsin primary said seven in 10 voters believed that U.S. trade takes more jobs from the state’s economy than it creates — an issue that could certainly resonate in the upcoming Rust Belt primaries.

Two of the three most populous states remaining on the primary calendar, Pennsylvania and Ohio, have seen heavy losses in the industrial sector in recent decades, and most of the free-trading coastal states already have held their primaries and caucuses. Though both must be careful not to provide ammunition to presumptive Republican nominee John McCain in the general election by veering too far into protectionism, the remaining primary calendar leaves little immediate incentive for either candidate to temper their trade rhetoric.

NAFTA could have particular potency in the March 4 Ohio primary, which many analysts see as a do-or-die contest for Clinton’s campaign. If Obama can attach Clinton to her husband’s trade agreement, he might cut into her long-held advantage with working-class white voters.

To that end, Obama has sharpened his trade talk — “She says speeches don’t put food on the table. Well, NAFTA didn’t put food on the table, either,” he said on Monday in Youngstown, Ohio — and he sent out mailers repeating a misleading accusation that Clinton said NAFTA was “boon” to the economy.

The quote comes from a 2006 article by the Long Island paper Newsday on Clinton’s trade stance. Obama and Clinton have identical voting records on trade issues, and both say NAFTA should be revisited to apply stronger protections for workers and the environment.

Clinton biographer Carl Bernstein told CNN that the then-first lady was a chief skeptic of the trade deal with Canada and Mexico.

“She argued with Bill Clinton when she was first lady ... she said ‘Bill, you are doing Republican economics when you are for NAFTA.’ She was against NAFTA,” Bernstein said.

Still, political experts say Obama’s tougher trade talk might work in Ohio, where the collapse of the manufacturing base remains a powerful political weapon in the hands of protectionists. Then-Rep. Sherrod Brown , a Democrat from a district running from Cleveland to Akron, rode a wave of populist fervor to victory over longtime Republican Sen. Mike DeWine in 2006.

“All throughout the Ohio valley,” Delano said, “trade issues and the concern over shipping jobs overseas rings loudly with voters,” Delano said.

“That is an issue that, even 15 years later (after passage of NAFTA), still resonates,” said Democratic Rep. Tim Ryan , D-Ohio.

Ryan would know.

He capitalized on union backing to unseat then-Rep. Tom Sawyer after a redistricting plan threw Sawyer into a district dominated by the hardscrabble Mahoning Valley on the eastern edge of the state. Once union voters there were reminded that Sawyer had voted for NAFTA nearly a decade earlier, he didn’t stand a chance.

“It’s that issue that transcends party and ideology,” Ryan said.

“It is potentially acute anywhere you have a collapsed manufacturing base, and that includes a lot of Ohio and a lot of other Rust Belt areas, but it requires a campaign to activate that issue,” said Justin Buchler, an assistant professor of political science at Case Western Reserve University in Cleveland.

But Obama could suffer a backlash if his effort is viewed as an unfair attack or waffling on his previous position on trade.

“I think a NAFTA effect won’t help her, but he’s, of course, been on both sides of the issue,” asserted Rep. Marcy Kaptur , D-Ohio, who, like Ryan, has not publicly committed her support to either candidate.

The Clinton campaign, citing news stories about his 2004 Senate run, has accused Obama of backtracking on previous support for NAFTA.

“It’s a judgment call,” Buchler said of Obama’s anti-NAFTA rhetoric. “It could work; it could backfire.”