Laying bare how dangerous it could be for Democrats to ignore populist opposition to corporate-friendly "free trade" deals, Republican presidential nominee Donald Trump on Tuesday attacked Hillary Clinton for her stance on trade in general and the Trans Pacific Partnership (TPP) in particular.

Speaking in Monessen, Pennsylvania, Trump said the "TPP would be the death blow for American manufacturing" and vowed to "withdraw" the U.S. from the agreement.

He said Clinton took "a leading part" in drafting the 12-nation deal, noting that the former secretary of state "praised or pushed the TPP on 45 separate occasions, and even called it the 'gold standard,'" according to prepared remarks.

"Hillary Clinton was totally for the TPP just a short while ago, but when she saw my stance, which is totally against, she was shamed into saying she would be against it too," he said. "But have no doubt, she will immediately approve it if it is put before her, guaranteed. She will do this just as she has betrayed American workers for Wall Street throughout her career."

With this claim, MSNBC reporter Alex Seitz-Wald wrote on Twitter, Trump appeared to be "speaking directly to [Bernie] Sanders supporters." Sanders has made opposition to the TPP and other rights-trampling deals a cornerstone of his campaign.

Trump also said he would renegotiate the North American Free Trade Agreement (NAFTA)—and placed partial blame for that deal also at Clinton's feet. "It was Bill Clinton who signed NAFTA in 1993, and Hillary Clinton who supported it," he said.

The real estate mogul's speech comes on the heels of the Democratic National Committee's platform drafting panel voting not to oppose the TPP, despite the fact that both Clinton and Sanders have come out against the deal. As Common Dreams reported, the Clinton-allied majority on the committee outvoted the Sanders delegates 10-5 to defeat the anti-TPP measure, citing President Barack Obama's support.

In doing so, argues Dave Johnson of the Campaign for America's Future in an op-ed Tuesday, they handed Trump "powerful ammunition" for his claims that Clinton is only "pretending" to oppose the agreement.

Johnson writes:

TPP and past "trade" deals are incredibly unpopular with working-class voters, and Republicans are preparing a full-scale attack on Clinton's credibility over the unpopular TPP. They are making the case that Clinton actually supports TPP but is pretending she does not in order to get votes. They say the president’s efforts to pass TPP in the post-election "lame duck" session back up their claims. This pro-TPP vote by Clinton supporters on the platform committee will likely bolster the Republican argument. [...] It appears that the party elite just don’t understand the public’s overwhelming opposition to TPP. The pro-TPP members of the platform committee say they must support a Democratic president. But what about the interests of the public, labor and working people, the environment, the economy and their own nominee?

In an interview with MSNBC's Andrea Mitchell on Tuesday, Sanders agreed that establishment voices on the committee appeared to not only be working against the party, but undermining Clinton's own stated position.

"I was really quite surprised to see that Secretary Clinton's delegates rejected our proposal to kill the TPP despite the fact that she has indicated she does not want to see it get onto the floor [of the U.S. Congress]," Sanders told Mitchell.

Meanwhile, as in the primary campaign, Clinton's refusal to come out swinging against corporate-friendly trade deals is costing her support of working-class voters in the general election—a dynamic Public Citizen's Lori Wallach predicted back in March, when she declared: "Americans' opposition to job-killing trade policies fueled the stunning Bernie Sanders upset victory in Michigan. But it also could be a deciding factor in the general election, especially with Donald Trump being the likely GOP nominee. The outcome of the Michigan primary shows the potency of trade issues and foreshadows the trouble Hillary Clinton could face winning key Midwestern states in a race against Trump."