Former Housing and Urban Development Secretary Julian Castro predicted that Americans in 20 years would ask what was "wrong" with President Trump when he expressed willingness to receive opposition research from foreign governments.

"I think you know, a few years from now -- whether it's 10 years from now, 20 years from now -- we're going to look back on this as Americans -- not Republicans or Democrats or liberals or conservatives -- and say 'What in the hell was wrong with that president?'" Castro, a 2020 hopeful, told Fox News during a town hall on Thursday.

Trump, on Wednesday, was criticized after he indicated that he would be willing to listen to foreign opposition research without notifying the FBI.

Castro added himself to the long list of Democrats criticizing Trump over those comments. House Speaker Nancy Pelosi, D-Calif., called Trump's remarks "appalling" and accused Republicans of trying to make money by staying silent about his "unethical" behavior.

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During Thursday's town hall, called Trump's remarks "unprecedented." "I think it's safe to say we have never seen that kind of moment in American history -- and that's not a good thing."

Fox News host Martha MacCallum had asked Castro about how Trump's comments were different from Democrats funding the controversial Steele dossier, which was compiled by a former British spy and used Russian sources.

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After Castro initially seemed to dodge the question, Fox News anchor Bret Baier pressed him on the perceived "double standard." Baier pointed to Brian Fallon, former spokesman for 2016 Democratic presidential nominee Hillary Clinton, saying he would have had "no problem" passing the Steele dossier along to reporters.

Castro responded by talking about a situation involving former Sen. John McCain, R-Ariz., and suggesting that people should move on from Clinton because she wasn't on the ballot for 2020.