The White House counsel's office in early November immediately notified the National Archives after documents with classified markings were found at an office Biden used in Washington, according to Garland. A Federal Bureau of Investigations review began a few days later. On Dec. 20 and then again this week, a personal attorney for Biden informed the Justice Department that more records were found at the president's home in Wilmington, Del.

The Trump probe began in reverse order, and saw the government taking escalating steps to force the former president to turn over documents.

The National Archives spent months trying to recover government records that it says Trump should have returned when he left office. Staff discovered documents with classified markings in boxes Trump turned over in January 2022, at which point they contacted the Justice Department. In court filings, prosecutors said Trump then tried to delay FBI access.

The Justice Department eventually issued a subpoena in May for any other classified materials at Mar-a-Lago. Trump's lawyers turned over another folder of documents in June, but prosecutors said the FBI had reason to believe there were more and got a search warrant from a Florida judge.

Trump and his Republican allies have taken an adversarial and often hostile stance toward the Justice Department's investigation, attacking the legitimacy of the probe, deflecting blame, and floating baseless conspiracy theories. His lawyers have maintained that he can't be criminally liable and suggested improper political motives are involved.

Biden and White House staff have struck a different tone; the phrase "cooperating fully" is repeatedly used. Intent can matter as prosecutors decide whether to prosecute a classified information case, and White House lawyer Richard Sauber released a statement saying they were "confident that a thorough review will show that these documents were inadvertently misplaced."

Cooperation can matter for other reasons. In the Trump probe, court documents showed that the Justice Department was not only investigating whether sensitive government information was mishandled, but also whether there was obstruction of justice. Bloomberg News previously reported that there are prosecutors who believe there are grounds to bring that charge against Trump.