In an interview for "Axios on HBO," Donald Trump Jr. told me he wants to debate Hunter Biden over who has benefited more financially from their father's government service.

Driving the news: "We can go full transparency, we show everything, and we can talk about all of the places where I am supposedly grifting but Hunter Biden isn't," said the president's eldest son, who still runs the Trump Organization with his brother Eric.

After I pressed Don Jr. on his book deal and paid speeches during Trump's presidency, he replied, "If you looked at my tax returns, which maybe we could talk about in this debate."

So you'll release your tax returns, I asked.

"If we do it both, 100%," Don Jr. said. "Let's talk about who profited off of whose public service. Happy to do it. Let's make it happen."

The other side: TJ Ducklo, national press secretary for the Biden campaign, said in response: "It is hard to believe anything a Trump says on tax returns when Donald Sr. has lied for years about releasing his."

Why it matters: After spending much of the past year aggressively attacking Joe Biden over his son's business dealings with a corrupt energy company in Ukraine while he was vice president, Republicans mostly stopped talking about Hunter when it looked like his father wouldn't make it through the primaries.

But now that Joe Biden has had a resurgence, Republicans are gearing up for investigations on Capitol Hill designed to undermine the vice president's chances in the fall.

What's next: Biden's allies have hit back, saying Democrats should fight fire with fire by subpoenaing Trump's children.

Former Obama aide Tommy Vietor tweeted: "The House Oversight Committee should start investigating the business dealings of Don Jr, Eric Trump, Ivanka and Jared. We should welcome a conversation about the children of corrupt politicians."

The bottom line: Don Jr. has now publicly embraced that conversation.

A source close to Don Jr. told Axios that his debate challenge was a direct response to "Biden allies, earlier in the week, threatening him and his siblings."

"From our point of view," the source added, "Don is already one of the most scrutinized people on planet Earth and is more than prepared to respond to Democrat attacks. The same can't be said about Hunter Biden."

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