TSA literally says on their own website that they are not looking for drugs and will only report it to the police if it's blatant.

TSA’s screening procedures are focused on security and are designed to detect potential threats to aviation and passengers. Accordingly, TSA security officers do not search for marijuana or other illegal drugs, but if any illegal substance is discovered during security screening, TSA will refer the matter to a law enforcement officer.

-source

I've watched a video about this recently. The problem is, most detectors were based on X-rays in the past decades. Liquid explosives are pretty close to the density (and/or other properties) of water, and you can't tell for sure whether there's toothpaste or boom juice in that tube.

However, some airports started using expensive ~~MRI~~ MRI like X-ray* machines that can see stuff in more detail, plus, it lets you to make cross sections from different angles and therefore have a 3D model that you can rotate on your screen (it's rather cool).

EDIT: I just realised someone else linked this, too. I would leave it here, it's still educational.