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Hillary Clinton's suggestion Monday that maybe Donald Trump doesn't pay income tax prompted the Republican candidate to interject: "That makes me smart."

The remark came in a segment about Trump's refusal to release his tax returns during Monday night's debate.

Donald Trump after Monday's debate. David Goldman / AP

The Democratic candidate seized on the controversial issue and offered a series of possible explanations for why the billionaire won't follow presidential-election precedent and release the returns.

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"Maybe he's not as rich as he says he is," Clinton offered up. "Maybe he's not as charitable as he claims to be."

She told the audience that it also could be because Trump isn't paying anything in federal taxes, noting that tax returns Trump was forced to disclose decades ago showed he had paid no federal income tax for some years.

"That makes me smart," Trump cut in.

Clinton later went on to say "maybe ... you haven't paid any federal income tax for a lot of years," and Trump appeared to cast further aspersions on paying taxes.

"It would be squandered ... believe me," he said.

Trump now gaslighting NBC, saying he didn't say that he didn't pay taxes and that it was smart (the whole country saw it) — Adam Servianski (@AdamSerwer) September 27, 2016

The remarks raised eyebrows on social media, with users questioning whether Trump was admitting to — if not bragging about — not paying taxes.

Trump: I'm smart because I didn't pay federal taxes.



Unclear that plays well with the average American. — ian bremmer (@ianbremmer) September 27, 2016

The Clinton campaign quickly seized on the moment with a tweet saying: "Paying zero in taxes doesn’t make you 'smart.' It makes you a tax evader."

Paying zero in taxes doesn’t make you "smart."



It makes you a tax evader. https://t.co/g9nQkSRvTB — Hillary Clinton (@HillaryClinton) September 27, 2016

When asked about the "smart" remark later, Trump told reporters he "didn't say that at all."

Trump has long refused to release his returns, saying he will do so when an IRS audit is completed. The IRS, however, has said there is no legal reason barring Trump from releasing them in the meantime.