GOP presidential nominee Donald Trump speaks at the Republican National Convention in Cleveland on July 21. Trump’s opposition to broad trade accords puts him at odds with much of his party. (Carolyn Kaster/AP)

Donald Trump is trying to reignite a debate over international trade in an effort to weaken Hillary Clinton’s support among blue-collar voters, particularly in Rust Belt states such as Pennsylvania, where the Democratic National Convention kicks off Monday.

In television interviews and on social media in recent days, Trump repeatedly attacked Clinton’s running mate, Timothy M. Kaine, for praising the Trans-Pacific Partnership, a sweeping trade agreement that has turned off activists in both parties. He also set out to remind voters that Bill Clinton signed the North American Free Trade Agreement, which the mogul argues has hurt workers in Pennsylvania and elsewhere.

Trump’s barrage comes as the Clinton-Kaine ticket is trying to iron out its differences and put up a united front on trade issues. A Clinton aide confirmed that the U.S. senator from Virginia has assured Clinton that he will soon voice opposition to TPP publicly. Clinton, who supported TPP as secretary of state, came out against it during the Democratic primary as she fended off a challenge from Sen. Bernie Sanders (Vt.), who opposes the deal.

At the same time as the Republican presidential nominee tries to stir discord in the Democratic Party, he has exposed a growing rift in the GOP. Trump’s opposition to broad trade accords puts him at odds with much of his party, including his running mate, Indiana Gov. Mike Pence. Some Republican officials complained that the way the GOP platform dealt with trade at last week’s convention was an affront to backers of free trade.

Trump has also drawn fire from the Clinton campaign, which has pointed to his business record as evidence that he is not the staunch defender of U.S. workers that he makes himself out to be, because many of his branded products are made overseas and he has made heavy use of foreign workers.

Hillary Clinton, the presumptive Democratic presidential nominee, and her running mate Sen. Timothy M. Kaine (Va.) appear at a rally in Miami on July 23. (Melina Mara/The Washington Post)

The result of the back-and-forth is a muddled picture in which both presidential candidates appear to believe they are in better position to cast themselves as champions of workers in states decimated by manufacturing job losses.

In an interview on NBC’s “Meet the Press” broadcast Sunday, Trump accused Kaine of being “in favor of TPP and every other trade deal that he’s ever looked at,” and he preemptively attacked Kaine’s expected opposition to TPP.

“He is going to change his tune. And I understand he’s now going to say, ‘I’m against TPP.’ Hillary Clinton was totally in favor of TPP, which is the job killer, right? So was he. When she watched me on your show and other shows, all of a sudden she changed, because she knows she can’t win that in the debate,” Trump said.

The mogul also fired off a series of trade-centric messages on his preferred social-media platform, Twitter.

“Funny that the Democrats would have their convention in Pennsylvania where her husband and her killed so many jobs,” Trump tweeted about the Clintons on Saturday. “I will bring jobs back!”

Kaine was one of 13 Democratic senators who joined most Republican senators to grant President Obama “fast-track authority” to push the TPP through Congress and has said positive things about it.

“I see much in it to like. I think it’s an upgrade of labor standards, I think it’s an upgrade of environmental standards, I think it’s an upgrade of intellectual-property protections,” he told reporters last Thursday, the day before Clinton tapped him as her running mate.

Clinton’s campaign on Sunday sought to play down the notion of disagreement between the two of them.

“Hillary Clinton is confirmed in her choice that her criteria for trade deals being met is they have to protect American workers, protect jobs, make sure that they don’t reduce wages, that they raise wages in America, protect our national security,” Clinton strategist Joel Benenson said on “Fox News Sunday.” “She is confident that Tim Kaine is in line with her on making sure any trade deal that this administration engages in will meet those criteria.”

Trump has said that as president he would withdraw the United States from TPP and seek to renegotiate NAFTA. He also advocates negotiating trade deals one-on-one with individual countries rather than groups of nations, which would be a dramatic departure from the regional approach favored by most trade experts.

While the mogul senses an opening against Clinton on trade, many pro-free-trade Republicans think Trump is picking a dangerous fight that threatens to upend decades of orthodox GOP beliefs.

“It’s absolutely troubling to see Republican candidates and the party demagogue a foundational issue like free trade,” said Tim Phillips, the president of Americans for Prosperity, a group backed by the billionaire industrialist Koch brothers. “We’ve clearly got long-term work to do to go back to the grass-roots base to deliver our message that free trade is the surest way to prosperity in society.”

The official party platform that was adopted at the GOP convention in Cleveland last week sounds very much like Trump’s talk on the campaign trail, causing some Republicans to worry the party has taken a protectionist bent.

“We need better negotiated trade agreements that put America first,” the platform reads. “When trade agreements have been carefully negotiated with friendly democracies, they have resulted in millions of new jobs here at home supported by our exports. When those agreements do not adequately protect U.S. interests, U.S. sovereignty, or when they are violated with impunity, they must be rejected.”

Rep. Kevin Cramer (R-N.D.), a Trump ally, said Trump’s talk on trade has spurred many in his party to reexamine their long-held views.

“I think for a lot of us Republicans who have taken default, traditional Chamber of Commerce positions, he’s provoked some consideration of ‘Maybe it doesn’t always have to be like this,’ ” Cramer said.

One of Trump’s top challenges will be to overcome charges by Democrats that he is being hypocritical. Clinton’s campaign has promoted websites and videos highlighting the fact that Donald J. Trump brand shirts and ties are made overseas in Bangladesh and China.

Trump’s plan is to try to stay on offense as much as possible. This week, that means trying to drive a wedge between Clinton and supporters of Sanders as the nation turns its attention to the Democratic convention in Philadelphia.

“Well, I’m not a fan of Bernie Sanders. But I am a fan of one thing that he talks about: trade,” Trump said on “Meet the Press.” He later added: “What happened with the choice of Tim Kaine was a slap in the face to Bernie Sanders and everybody.”