Thomas Matthew Crooks Seen Getting Bullied in School in Newly Surfaced Video

The 20-year-old who tried killing Donald Trump is said to have been a black sheep and a loner who would get bullied in school -- and now, we have video showing exactly that.

Thomas Matthew Crooks was filmed on camera a few years ago while he was in high school -- and the footage, which has surfaced online, shows him being hassled in class by another student. TMC is sitting at his desk ... and you can see somebody yanking on his pant leg.

The person who's tugging at his pants seems to be trying to straight up pull him out of his seat -- and although it looks playful in nature ... you can even hear someone off-camera saying "stop" repeatedly.

It seems like that person is Thomas himself ... and he later notes that his leg is being bothered. There are other people who can be heard on camera laughing at all this.

The whole scene jibes with what multiple reports about Thomas from other classmates -- who say he was a bit of an outcast and someone who'd constantly get picked on by others. There's also been reports that Thomas tried getting on his school rifle team, but was rejected ... because apparently he was a terrible shot.

Everyone is digging into this guy's background ... and more and more is coming out by the hour -- but this video is revealing, as it does appear to show someone who wasn't the most popular.

In terms of whether this played into his motivation at all ... the jury's still out -- the feds are looking into what might've led Thomas to do this, but not much is know at the moment.

One thing that is going around about him -- he was a registered Republican, but he made a donation to a left-leaning PAC ... so even his political affiliation is murky at this point.