Four people serving at the very top of the US government - Donald Trump, Joe Biden, Hillary Clinton and Mike Pence - appear to have mishandled classified materials. How do their cases differ?

Mr Trump is in the deepest trouble. He has been indicted on 37 charges related to files found at his Florida home.

His supporters are pointing to the examples of Joe Biden and Hillary Clinton as a double standard applied to Democratic politicians.

This is how all these cases compare.

More than 325 classified files - including some marked with Secret and Top Secret designations - were discovered over the course of last year at Mr Trump's Mar-a-Lago estate.

Aides to Joe Biden discovered classified documents in Washington and at his Delaware home.

Former Vice-President Mike Pence also made headlines when documents were found unsecured at his home in Indiana. The US Department of Justice told him recently they are not pursuing charges.

Those three discoveries were within a few months of each but the classified material saga concerning Hillary Clinton goes back a few years.

She used a personal email address while working as secretary of state from 2009-13 under President Barack Obama. This meant some classified material was shared on her server at home, which was unsecured.

The National Archives initiated contact with Mr Trump's office after determining that it did not have possession of some notable records from his presidential term.

The former president's team provided some material but the archivists did not believe they had been fully co-operative.

That set in motion the FBI inquiry that led to a surprise search of the Mar-a-Lago estate and the discovery of more than 100 additional documents.

Mr Biden's personal lawyers discovered his classified documents as they were moving his stuff out of an office he used at a think tank in Washington.

The following day, they turned what they found over to the National Archives and the FBI conducted their own search and found more. A second trove was found a few weeks later at his Delaware home.

Mrs Clinton's use of a private email first came to light in March 2016 after she had quit her job as secretary of state to run for president.

Her team handed over nearly 60,000 pages of emails but also deleted more than 30,000 emails they said were deemed to be personal in nature.

Mr Trump and Mr Biden both have a special counsel looking deeper into what they did wrong.

Under the Presidential Records Act, White House records are supposed to go to the National Archives once an administration ends. Regulations require such files to be stored securely.

Jack Smith, a former war crimes prosecutor, has brought an indictment against the former president, who faces dozens of counts of unauthorised possession of classified material, obstruction of justice, concealing documents and making false statements to law enforcement

A Trump-appointed prosecutor Robert Hur is looking into the Biden case, which is still ongoing.

The FBI described Mrs Clinton's actions as careless but said there was no case for a "reasonable prosecutor" to bring.

Mr Pence was told last week by the US justice department that they are not pursuing charges.

According to the indictment, the documents found at Mr Trump's Florida home were highly sensitive.

They include details of US nuclear weapons programmes, the potential vulnerabilities of the US and its allies, and US plans for retaliatory military attacks.

They were found in boxes in various rooms in Mar-a-Lago, including a storage room, two ballrooms and a bathroom, tucked between a shower and a toilet.

The documents discovered in Mr Biden's office were marked "sensitive compartmented information", according to CNN, indicating the material could involve intelligence-gathering methods and sources.

They reportedly included information about Ukraine, Iran and the UK and dated from his time as vice-president and, before that, senator.

The FBI said there were 113 Clinton emails which contained classified information but they did not reveal the nature of them.

There are 31 counts against the former president of "wilful retention of national defence information".

This means prosecutors believe he knew that what he was doing was unlawful, and they have recordings of him apparently speaking about that and the testimony of witnesses.

It also alleges that he showed some of this material to people without the required security clearances.

In the Clinton case, FBI Director James Comey decided after an investigation that she had been careless in using a private server but it was not intentional.

Mr Trump is also accused of obstructing the investigation. But he says Mrs Clinton destroyed evidence and points to the deleted emails. At one press conference, he even urged Russia to find them.

In Mr Comey's view there was no cover-up, even though an FBI investigation found many of the deleted emails were work-related.

Not enough is yet known about the investigation into President Biden to make a comparison.

Mr Trump has accused the FBI and the justice department of pursuing a politically motivated investigation in an effort to prevent him from running for the White House again.

Mrs Clinton testified to Congress about her email server as part of the Benghazi hearings, and it came up regularly during the 2016 election campaign.

She said she fully complied with the investigation and handed over all work-related emails after her team had gone through a "thorough process".

Mr Biden, for his part, said Mr Trump's handling was "totally irresponsible" after the news first emerged, opening himself up to accusations of hypocrisy weeks later.

The president has said he was "surprised" there were sensitive documents at his former office and that he is co-operating fully with the review.

Mr Pence always maintained the documents had ended up at his home "inadvertently" but he had taken full responsibility for the mistake.