For top US officials, it appears the words "top secret" are sometimes treated as more of a suggestion than a rule.

Former US Vice-President Mike Pence is the latest in a long line of politicians to have classified documents turn up at his home.

Both President Joe Biden and former President Donald Trump are currently facing investigations into files found in their possession.

Mr Pence and Mr Biden notified authorities when the documents were discovered. The FBI raided Mr Trump's Mar-a-Lago estate to recover classified and sensitive material, with officials citing alleged obstruction by the Trump team.

But they are far from the first politicians to be found potentially mishandling sensitive material.

From Hillary Clinton's emails to a Canadian minister's resignation, many statesmen have landed in trouble for not following security protocols.

"Misplacing classified documents is very common, happens all the time," said Tom Blanton, who runs the National Security Archive, an independent repository of government documents based at George Washington University.

Should more documents be declassified?

While it is unclear exactly what was in the documents Mr Pence had in his possession, Mr Blanton said there is a wide range of information that can be classified. Some materials, like travel briefings, may be classified even if they contain mostly public information from news articles.

Such files are supposed to be declassified after a period of time, but because it does not automatically happen, there is inevitably a backlog - which is partly why officials are "drowning" in classified information.

Other classified documents, labelled "Sensitive Compartmented Information" (SCI), contain details that could expose intelligence sources.

Several documents marked SCI were found at Mar-a-Lago, Mr Trump's Florida home, according to photos released by the FBI.

Are Trump's documents different?

But the big difference between others' missteps, and Mr Trump's, is how the mistakes were handled after they were discovered, says national security legal expert Brad Moss.(BBC)