Both the 45th and 46th Presidents appear to have absconded classified documentation to their private residences or locations that pose legal issues and/or national security concerns.
Here is some background information about classified documents that might be helpful to you as you peruse the news on the subject and make up your own mind about what has happened.
SCIF: Sensitive Compartmentalized Information Facility.
Typically, this is a physical location (room, building, etc) with specific physical security measures to keep classified information safe. Those with access can view, store, print, or otherwise access the products. The Congressional SCIF (I presume) is just for viewing...Not sure where the committees that have access actually do their work, which would probably create classified documents.
SCIFs are rated for the classification level of information they contain. All of these locations have strict access requirements including the appropriate clearance, access lists and badges, no mobile devices, earbuds, smart watches, etc.
TS - Top Secret (exceptionally grave damage to National Security)
S - Secret (grave damage to National Security)
CUI - Controlled Unclassified Information (replaced For Official Use Only - FOUO) and includes things like personally identifiable info, or other things that we generally want to keep private, but aren't strictly classified.
Another way to accidentally attain a higher classification is by adding multiple pieces of unclassified information together. This is one of the things we have to be careful of, because if you're not careful, the final document might be a higher classification because of the sum of its parts.
Classification markings are not only on the cover sheet, but also throughout the document itself, including pages and individual paragraphs.
Classified documents generally have to stay inside SCIFs. Documents can only come out if properly packaged to protect the information and then are carried by official couriers with special training, clearances, and lockable courier cases. Not quite a briefcase with handcuffs, but close.
There are classified computer networks which have no connection (air gaps) to the regular internet or outside world. These are essentially completely securely self-contained and handle information up to a particular classification level; so, there are secret systems as well as top secret systems. TS can handle any level up to TS (including secret). Secret can only handle up to secret info. These systems include email clients so you can send documents to other users with access and need to know.
There are also unclassified computer systems for daily work that have internet connectivity but are regulated by IT policies and systems that filter what you can get to. E.g., for the longest time, Al Jazeera News wasn't accessible on the unclassified network.
Also, all users sign acceptable use policies as a prereq to getting network access, and sites that are forbidden in the AUP are routinely blocked; so if there's a bad link on the page (site, video, etc.), you'll often get an intimidatingly official looking "ACCESS TO THIS SITE IS FORBIDDEN" in that space. Sometimes it's the whole page.
Getting a Clearance.
How one gets a security clearance is another saga that includes a veritable colonoscopy of background checks going over years of your past, personal connections, rap sheets, foreign travel, credit score and finances, past addresses, scrutiny of your family and much more including an in person interview, and if required, possibly a polygraph. Good times.
Clearances are also re-vetted periodically to make sure the person is still considered safe to have a clearance. It used to be that clearance reviews only happened every 5 or 10 years (depending on the clearance level), but they're changing that to "continuous vetting" now where the security apparatus overseeing this will be alerted to things like criminal offenses, bankruptcies, other "derog" (derogatory) information; one can presume that they're closely looking at social media and such as well.