Top Republicans on the House Judiciary Committee demanded all relevant documents and communications between the department, the FBI, the White House and Biden's attorneys. They said the Justice Department's appointment of Robert Hur as special counsel for the case this week raised "fundamental oversight questions." 

Despite the letter, former assistant U.S. Attorney Reid Schar - now a partner at Jenner & Block - said Hur has a reputation for being independent and fair.

"He is perceived both within the department and more generally in the public sphere as someone who is not going to be particularly favorable to a Democratic president but, at the same time, someone of the utmost integrity who is not going to pursue anyone just because of a political affiliation."

Hur will investigate whether the classified records from Biden's time as vice president had been improperly stored - a situation that echoes a wider-ranging inquiry directed at former President Donald Trump's handling of classified documents.

But legal experts say their cases are not the same.

Trump resisted returning the papers, forcing an FBI search that turned up about 100 classified documents, and raising questions about whether Trump or his staff obstructed the investigation.

The White House, in contrast, said Biden's attorneys found a small number of classified documents and turned them over after they were discovered. 

Schar said the criminal statute involved requires intent, and the comments by Biden's team is likely to signal the defense strategy.

"I think that's part of an argument you can see coming, which is, 'We didn't know we had these. We certainly didn't intend to take them. And as soon as we found them, we raised our hand and we tried to return them as quickly as we could.' And that's all driven by trying to make clear that there was no intent to to have these classified materials and therefore no violation of the statute."

The inquiry is a distraction for the Democratic president, who has criticized his Republican predecessor's handling of classified material, and could cast a shadow over Biden as both men gear up for a possible 2024 election rematch.