May 25, 2017 11:25 AM EDT

Earlier this week, news started circulating that President Trump’s proposed budget was based on a math error, a very large one, too. “It turns out that the entire budget is based on a $2 trillion math error,” said Stephen Colbert on Wednesday night’s episode of The Late Show. While theoretically the budget is meant to boost economic growth enough to pay for $2 trillion in spending within 10 years, critics say it contained an accounting error that adds up to a $2 trillion oversight.

Colbert had an idea about the source of the questionable computing. “There is a simple explanation for how this happened: Donald Trump is an idiot,” Colbert quipped, adding another possibility into the mix: “Or, he’s lying.”

While White House Budget Director Mick Mulvaney stands by the numbers in the budget, saying during a press briefing, that the double counting was done “on purpose” because “you don’t want to make too many assumptions.”

Colbert was not impressed with the explanation, retorting: “You don’t want to make assumptions because when you assume, you make an a– out of you, Mick Mulvaney.”

Watch the full clip below.

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