I worked alongside a bunch of pathological liars once. One ran the company; he hired the others. It was when I was young enough to learn from it. When you spend a couple years around people with that inability to differentiate truth from fiction, the tells are very clear.

It has saved me a lot of pain since! I can smell them from a long ways away, and I developed effective strategies to resist getting sucked in. It’s not a plan on those people’s parts; they aren’t trying to lie. But they often wind up manipulating other people to cover for them.

So when that person is (sometimes) called to task for everything they said, it can pull a network of current and former friends, many of whom don’t even know that the person was lying to them or that they lied on their behalf! It’s ugly.

FYI: the major tells are:
• Too good to be true stories
• Tells a secondhand story or urban myth as first person
• Every time they tell the story, details differ
• When challenged on any story, they have an explanation that may not be credible as to why they spoke in error

For instance: https://www.thecut.com/2018/05/how-anna-delvey-tricked-new-york.html

Some people claim to be the inventor of a technology that they are not (a la the white lie in “Romy and Michele's High School Reunion," but for real). Like he claims he invented a basic Internet technology, for instance.

Trump is a compulsive liar, maybe not pathological, because it seems pretty clear that at least earlier in life, he simply said anything he felt he could get away with. In depositions, when challenged, he would ultimately admit the truth, so he *knew* the truth (at least then).