The first presidential debate between Hillary Clinton and Donald Trump opened with an intense back-and-forth about an issue that has been all but invisible on the national stage for two decades: trade.

Trumps trade plan is vague and politically improbable , but he smelled blood on the issue Monday night. He repeatedly hammered Hillary Clinton over her support for the North American Free Trade Agreement a pact negotiated by President George H.W. Bush and signed into law by Bill Clinton in 1993.

NAFTA is the worst trade deal ever signed in the history of this country, Trump said in the debates opening minutes.

After spending months talking constantly about trade, Trump also credited himself for bringing the issue to the forefront of the campaign. He accused Clinton of not thinking about solutions to the countrys trade imbalance until his campaign created a movement. He told her to travel to the post-industrial pockets of the country and see the devastation.

In all fairness to Secretary Clinton, shes been doing this for 30 years, Trump said. Why hasnt she made the agreements better?

Look at Ohio, Trump went on, noting perhaps the most crucial swing state in the election. All these places where so many jobs their companies are leaving.

We have people that are political hacks, negotiating our trade deals, he said.

Both Clinton and Trump are on record opposing the Trans-Pacific Partnership, the mammoth deal brokered by the Obama administration that involves a dozen countries. That particular trade deal was an arcane policy debate until it became the sleeper issue of the presidential campaign. Trump has put the deal squarely in line with NAFTA, while Clinton has said that it doesnt meet her standards and that she would oppose it as president.

But, as Trump noted, Clinton had alluded to an early iteration of the TPP as the gold standard of trade deals, while she was serving as secretary of state in the Obama administration. The candidate tried to yoke those words to his opponent repeatedly on Monday.

You called it the gold standard, Trump burst, cutting off a response from Clinton. You called it the gold standard of trade deals.

Clinton defended herself by saying she analyzes each trade deal on the merits and voted against the Central American Free Trade Agreement during her tenure in the Senate. Hinting at her vulnerability on this issue, she said, Lets not assume trade is the only challenge we have in the economy, before blasting Trump for making an expensive slate of tax cuts for the super-rich a central tenet of his economic agenda.

Clinton scoffed at Trumps claim that she was following his lead politically on trade.

Well, Donald, you live in your own reality, but it is not the facts, she said.

Throughout the campaign, Trump has bucked Republican orthodoxy with his fierce opposition to trade deals, while toeing the GOP party line on tax cuts for the wealthy. On trade, he has sounded less like a representative of the party of Reagan and more like Clintons primary opponent, Sen. Bernie Sanders (I-Vt.), a self-described democratic socialist echoing critiques that have long been voiced by labor unions, tinged with a more aggressive nationalism that resonates with his own anti-immigrant views.

Republican leaders and Democratic presidents have long supported the free-trade dogma that Trump and Sanders have railed against. Whatever the policy diagnosis, both Trump and Clinton would be hard-pressed to reverse 30 years of global economic stewardship with Republicans in control of at least one chamber of Congress.

Editors note: Donald Trump regularly incites political violence and is a serial liar , rampant xenophobe , racist , misogynist and birther who has repeatedly pledged to ban all Muslims 1.6 billion members of an entire religion from entering the U.S.