WASHINGTON (AP) — Security-sealed rooms. Lock bags. And in the most rare of circumstances, the ability to handcuff a document pouch to a messenger to transport the nation’s secrets.

These are some of the ways Capitol Hill keeps classified documents secured, an elaborate system of government protocols and high-level security clearances that stands in stark contrast to the storage room stash of secrets at Donald Trump’s Mar-a-Lago estate in Florida.
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... Capitol Hill, where 535 elected members of Congress, alongside thousands of aides and countless more visitors broker information on a daily basis as a routine part of governing. 

Yeah, and that's pretty stark too. 535 MC's; one POTUS.
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But when it comes to classified materials, the stream of information tends to clamp shut.
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When members of Congress want to peruse classified materials, they descend deep into the basement of the Capitol to a sensitive compartmented information facility, known as a SCIF. Other SCIFs are scattered throughout the Capitol complex.

If documents need to be ferried in or out of secure locations, they are typically transported in a lock bag, a briefcase-sized pouch under lock and key.

Sen. Bob Casey, D-Penn., a member of the Intelligence Committee, said staff will often use a lock bag even simply to transport materials from committee offices to a SCIF some 30 feet (9 meters) away.

“The idea that anyone would leave any building or any room with those documents not secure — it’s just, the word is, unfathomable,” Casey said in an interview.
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Sen. Martin Heinrich, D-N.M., all but warned of Trump’s handling of sensitive documents early in the then-president’s term. A photo from a White House press briefing in 2017 showed Trump and others in the Oval Office with a lock bag visible on the desk, the key still inside.

“Never leave a key in a classified lock bag in the presence of non-cleared people. #Classified101,” tweeted Heinrich, a member of the Intelligence Committee, days after the February 2017 incident. He asked for a review.

In an interview this past week, Heinrich said, “It is outrageous to think — the cavalier nature with which the former president treats information, that can have life or death consequences for our sources, is unfathomable.”

...Trump attorneys had insisted early in the summer after the first delivery of returned documents that there was nothing left at the former president’s club. Upon inspection, the FBI asked the storage room to be put under lock and key. Ultimately a search warrant for Mar-a-Lago was obtained and more than 100 other documents with classified markings were found.
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Retribution for breaking secrets on Capitol Hill can be swift and severe. In the 1980s, Sen. Patrick Leahy, D-Vt., announced he would leave the Intelligence Committee after acknowledging that he had allowed a reporter to review a not classified but still “committee confidential” draft report on the Contra wars in Latin America. More recently, a former senior staff member of the Senate panel was charged with lying to investigators about his interactions with journalists. 

The difference in consequences is stark, too.