Donald Trump. Kevin Lamarque/Reuters President Donald Trump reportedly instructed his staff to portray him as "crazy" to get more out of trade negotiations with South Korea.

Trump gave the advice to his top trade negotiator, Robert Lighthizer, during an Oval Office meeting with top officials in September, according to an Axios report on Sunday that cited people familiar with the conversation.

The group was discussing whether to pull out of a free-trade deal with South Korea, a threat Trump has floated since early September. Trump then began coaching Lighthizer on how to proceed, according to the sources who paraphrased the exchange for Axios:

"You've got 30 days, and if you don't get concessions then I'm pulling out," Trump told Lighthizer. "Ok, well I'll tell the Koreans they've got 30 days," Lighthizer replied. "No, no, no," Trump interjected. "That's not how you negotiate. You don't tell them they've got 30 days. You tell them, 'This guy's so crazy he could pull out any minute.'"

Trump continued: "That's what you tell them: Any minute. And by the way, I might. You guys all need to know I might. You don't tell them 30 days. If they take 30 days they'll stretch this out."

Some national security experts have criticized Trump's apparent willingness to foster a "madman" image with world leaders, especially with regard to North Korea. The president has vowed to "totally destroy" the country and has referred to its leader Kim Jong Un as "Rocket Man" on several occasions.