Former Mexican President Vicente Fox said Tuesday that President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE never learned the difference between running his company, the Trump Organization, and what it takes to run the United States.

“When you move from business and private sector into politics, you have to go through a process,” Fox said on Comedy Central's “The Opposition With Jordan Klepper.” "This guy doesn’t have any idea of the difference between running a nation and running a business.”

"He's only a mediocre businessman," Fox added, to cheers from the audience.

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Fox has been a top critic of the president over Trump's immigration policy, particularly his plans to build a wall on the Mexican border while making Mexico pay for it.

“I said, 'I’m not paying for that f---ing wall,' ” Fox repeated Tuesday.

Fox has frequently attacked Trump both on Twitter and on camera, frequently using profanity and personal attacks to make his point. In November, the Mexican politician mocked Trump over reports that Secretary of State Rex Tillerson Rex Wayne TillersonGary Cohn: 'I haven't made up my mind' on vote for president in November Kushner says 'Alice in Wonderland' describes Trump presidency: Woodward book Conspicuous by their absence from the Republican Convention MORE had referred to his boss as a "moron."

"I think it's fake news, but if he did that, I guess we'll have to compare IQ tests," Trump said at the time of the reports Tillerson used the word.

"@realDonaldTrump don't take that IQ test," Fox tweeted in response. "Just answer this: You know the name of North Korea's leader, right? Is it -Un or is it -Il?"