Joe Biden said his son did nothing wrong while serving on the board of a Ukrainian gas company while the former vice president was serving under the Obama administration.

In an interview with CBS Evening News, the 2020 presidential candidate said he did his job without any concern about his son Hunter's role with Burisma.

"I don't tell my grown son what he can do, as long as whatever he's doing is appropriate," Biden said.

The host pressed Biden on whether he considered the optics of his son working for a Ukrainian company during his years in the White House. Biden contended that Hunter was already on the board when he took office.

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"And he's a grown man," Biden said. "And it turns out he did not do a single thing wrong, as everybody's investigated."

Hunter Biden was reportedly paid $50,000 to $80,000 a month for several years while serving on Burisma's board. The host asked the former Delaware senator about Hunter's claim that the only thing his father said to him about the job was, "I hope you know what you're doing."

"What I meant by that is I hope you've thought this through," Biden said. "I hope you know exactly what you're doing here. That's all I meant. Nothing more than that because I've never discussed my business or their business, my sons' or daughter's. And I've never discussed them because they know where I have to do my job and that's it and they have to make their own judgments."

In response to President Trump's ongoing calls to investigate his son further for his work with the company, Biden leveled his own challenge.

"Mr. President, release your tax returns. Let's see how straight you are, OK old buddy?" Biden said. "I put out 21 years of mine. So show us your tax returns, bud. What are you hiding? You want to deal with corruption? Start to act like it. Release your tax returns or shut up."