President Obama hit presumptive GOP presidential nominee Donald TrumpDonald John TrumpTrump says 'Failing New York Times' should be held 'fully accountable' over Russia report Trump says 'Failing New York Times' should be held 'fully accountable' over Russia report Trump tweets ICE will begin removing 'millions' of undocumented migrants MORE for not detailing the ways in which he plans to accomplish certain goals.

During a PBS town hall that aired Wednesday, Obama referenced Trump's promise to bring back jobs to the United States when talking about manufacturing.

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“Well, how exactly are you going to do that? What exactly are you going to do? There’s no answer to it," Obama said.

"He just says, 'Well, I’m going to negotiate a better deal.' Well, what, how exactly are you going to negotiate that? What magic wand do you have? And usually the answer is, he doesn’t have an answer.”

Obama has slammed Trump in the past. 

During a speech Wednesday, the president bashed one of the candidate's central arguments that international trade and immigration have hurt American voters. He called Trump's pledge to roll back Wall Street regulations "crazy."

"That will not help us win," Obama said of Trump. "That is not going to make your lives better." 

Trump often talks about bringing back manufacturing jobs while on the campaign trail and pledges to place tariffs on companies that move outside of the country.