President Joe Biden is facing intense scrutiny after batches of classified documents dating from his vice presidency were found in his former think-tank office in Washington and in his Wilmington, Del., home, sparking a Justice Department investigation and prompting Attorney General Merrick Garland to appoint Robert K. Hur as special counsel to investigate.

Garland announced the appointment two months after he named a different special counsel to oversee the criminal probe of former president Donald Trump’s handling of classified information.

Elected officials’ handling of sensitive government material has been the subject of fierce political debate in recent years — drawing public attention to the way classification, a bureaucratic process that’s a staple in Washington, actually works.

Here are the basics.

What is a classified document?

Classified information refers to documents and other records that the government considers sensitive. Access is generally restricted to people who have passed the proper background checks and have been granted security clearances. Authorized government officials classify information when they conclude that its release could damage U.S. national security or foreign relations.

Classified information can include paper documents, emails, photographs, maps, images, databases and hard drives. Regardless of the medium, classified information requires protection until it is formally declassified.

This image contained in a court filing by the Department of Justice on Aug. 30, 2022, and redacted by in part by the FBI, shows a photo of documents seized during the Aug. 8 search by the FBI of former President Donald Trump’s Mar-a-Lago estate in Florida. For years, problems with classified materials have been a shortcut to controversy in Washington. Department of Justice via AP

What are the three main levels of classified information?

There are three broad levels of classified information.

Confidential is the lowest category of classified information and refers to information that could damage national security if publicized. The largest number of government workers and contractors — thousands of people — have access to this information. Examples might include basic State Department cables or information provided by a foreign government. “Even if it doesn’t involve highly sensitive secrets, it would be marked as confidential,” said Steven Aftergood, a longtime specialist in the handling of classified information. “And you do not want to release it, because it would complicate diplomatic relations with that foreign government.”

Secret is the next level of classification, referring to material that, if released, could cause “serious damage” to national security. This is the broadest category, including, for example, the budget of a U.S. intelligence agency.

Top secret is the most sensitive information bracket, covering records that could cause “exceptionally grave damage” to national security if released. Such damage could include revealing intelligence on armed hostilities against the United States or its allies, disruption of vital foreign relations or the compromise of defense plans or intelligence gathering.

Within “top secret” exist a number of subclassifications, often dealing with the most protected pieces of American information and intelligence. Falling under this classification is sensitive compartmented information, a designation that limits dissemination to a particular group of people. This includes information derived from secret sources and closely guarded intelligence methods. It could also be intelligence gleaned from an electronic intercept or information provided by an informant in a foreign country.

“The concern there is that if it were disclosed, then not only would national security be at risk but the individual source or method could be, too,” Aftergood said.

How are classified documents labeled?

According to the National Archives, the federal government’s system of marking and controlling security-classified information dates from World War II. It is generally any information that “would damage national security if improperly released.”

Modern classified documents are marked as such at the top and bottom of each page, and in some cases paragraphs may contain notations that information contained within has been downgraded to secret or confidential. Declassified documents are marked with a stamp, along with the name of the person and office that authorized the action.

How is information classified? How long do documents stay classified?

In theory, the U.S. president gets to decide what information is classified and what is not.

In practice, the president delegates the responsibility to Cabinet and agency heads, who then may give the responsibility to others who work for them.

“Throughout the executive branch, there are a few hundred officials who can generate and designate it,” Aftergood said.

Information remains classified “as long as required by national security considerations,” according to government guidelines. Sometimes a specific date or event might be set for declassification. Classified status can also be extended by authorized individuals.

The president also has the authority to declassify information, generally as soon as national security considerations permit. Typically, there is a process for doing that, notably by consulting the Cabinet secretary or agency head whose department originated the information to ensure that declassifying it poses no risk to national security.

Who can access classified information?

Government workers and contractors must go through background checks to receive the necessary clearance to access classified information. The more sensitive the information, the more arduous the background check.

But that isn’t to say that access is rare. According to an Office of the Director of National Intelligence report from 2019, the last year for which data was published, nearly 3 million people had access to confidential or secret documents. More than 1.25 million people had been issued clearance for top-secret documents.

Some classified information is shared among thousands of people. For other information, only a handful of officials have the necessary clearance levels to access it. The president has access to every document and all intelligence information.

Some officials have to sign nondisclosure agreements when they leave the government to ensure they do not discuss the secret information they had access to while on the job.

In general, classified information also needs to be housed in what is known as a sensitive compartmented information facility (SCIF) that has appropriate controls to ensure security.

What is the penalty for mishandling classified information?

Various federal laws, including portions of the Espionage Act, make it illegal to remove, disclose or destroy classified information. Violations carry punishments ranging from three to 10 years in prison and hefty fines.

Government officials who have been accused of mishandling classified information include David H. Petraeus, a former Army general and a CIA director during the Obama administration, and Samuel R. “Sandy” Berger, a national security adviser in the Clinton administration. Both pleaded guilty to misdemeanor charges for unlawfully removing secret documents.

How do Biden’s situation and Trump’s compare?

There are a few early distinctions between the Justice Department’s review of the documents found at Biden’s home and former office and the agency’s ongoing criminal investigation of Trump’s handling of classified documents.

Volume is one key difference. The FBI eventually recovered more than 300 classified documents from Trump’s private club and residence, Mar-a-Lago, last year, according to government court filings. At least 10 documents were found in Biden’s Washington think-tank office. It appears one classified document was found at the president’s Wilmington home.

Another contrast is that the classified materials found at Biden’s home and former office were swiftly and voluntarily returned to government custody, his lawyers have said. Trump resisted government entreaties to hand over official documents for months, including after a grand jury subpoena demanded the return of any material marked classified.

In Trump’s case, investigators are looking at possible charges of obstruction of justice or destruction of records by him or others, as well as the possible mishandling of government secrets. No such allegation has been leveled in the Biden matter, but the investigation is at an earlier stage.

But the irony has not been lost on GOP critics of the president. Biden, in a September television interview, called Trump’s handling of classified documents “totally irresponsible,” asking, “How that could possibly happen?”

On Thursday, before Garland’s announcement of a special counsel, Biden told reporters he takes “classified material seriously,” adding that his staff is “cooperating fully with the Justice Department’s review.” The president suggested he would say more on the matter in the near future.

The Washington Post’s Glenn Kessler contributed to this report.