Jill Colvin and Lisa Lerer

MONESSEN, Pa.: Donald Trump called for a new era of economic “Americanism” Tuesday, promising to restore millions of lost factory jobs by backing away from decades of U.S. policy that encouraged trade with other nations — a move that could undermine the country’s place as the dominant player in the global economy.

In a 35-minute address, Trump threatened to exit the more than two-decade old North American Free Trade Agreement and vowed to withdraw from the Trans-Pacific Partnership, an agreement among 12 Pacific Rim nations that has yet to take effect.

He blamed many of America’s economic woes on China, promising to label the country a currency manipulator and slap new tariffs on America’s leading source of imports, a decision with the potential to dramatically increase the cost of consumer goods.

The speech marked a significant break from years of Republican Party advocacy for unencumbered trade between nations, and drew immediate condemnation from GOP business leaders. Trump blamed the policies of Democratic rival Hillary Clinton and her husband, former President Bill Clinton, for the loss of millions of manufacturing jobs.

“This wave of globalization has wiped out totally, totally our middle class,” Trump said, standing in front of pallets of recycled aluminum cans on a factory floor. “It doesn’t have to be this way. We can turn it around, and we can turn it around fast.”

Delivered in a hard-hit Pennsylvania steel town, the speech underscored the central message of Trump’s campaign: that policies aimed at boosting international trade — and America’s intervention in wars and disputes abroad — have weakened the country.

It’s an argument that found support among Republican primary voters, especially white, working class Americans whose wages have stagnated in recent years. Trump hopes it will yield similar success among the wider electorate that will decide the general election.

“I promise you, if I become president, we’re going to be working again. We’re going to have great jobs again,” he said. “You’re going to be so happy.”

But many economists have dismissed Trump’s promise to immediately restore manufacturing jobs as dubious at best, given the impact of automation and the many years it typically takes to negotiate trade agreements.

While renegotiating tougher deals with America’s foreign trading partners might help some businesses, manufacturing as a share of total U.S. jobs has been slipping for several decades. The number of such jobs has risen slightly since the end of the Great Recession, but the introduction of robotics and access to cheaper foreign markets has reduced U.S. factory employment to a total last seen around 1941.

Indeed, the National Association of Manufacturers slammed Trump’s logic on Tuesday, with the organization’s president, Jay Timmons, writing on Twitter: “@realDonaldTrump you have it backward. Trade is GOOD for #mfg workers & #jobs. Let’s #MakeAmericaTradeAgain.”

Tuesday’s speech drew a scathing response from the U.S. Chamber of Commerce, a traditional Republican ally and leading business lobby.

“Under Trump’s trade plans, we would see higher prices, fewer jobs, a weaker economy,” the Chamber said on its Twitter feed, directing readers to a blog post that said Trump’s policies would lead to millions of job losses and a recession.

Democrats, meanwhile, didn’t wait for Trump to start talking before they jumped in to slam his ideas, detailing all the products his companies make overseas in a conference call with reporters.

“I’ll give Donald Trump this. On trade, with all of his personal experience profiting from making products overseas, he’s the perfect expert to talk about outsourcing,” said Ohio Sen. Sherrod Brown, a Clinton supporter. “Trump doesn’t make things in America.”