Trump's 2016 campaign amassed a database of millions of voters in swing states and Matthew Brian Crooks was one of them ... with Trump's team determining he was a likely gun owner and "hunter" who would favorably respond to pro-gun rights messaging ... according to data first obtained and revealed by the UK's Channel 4 News.

The would-be assassin's mother, Mary, was profiled by Trump's 2016 campaign too apparently ... and she was also identified as a likely gun owner by campaign researchers.

And get this ... Trump's campaign database assigned scores to each of the 6.7 million Pennsylvania voters analyzed ahead of the 2016 election ... with the shooter's father scoring among the top 20 in their Bethel Park hometown in terms of pro-gun-related indicators.

Crooks' father legally purchased the AR-15-style rifle his son used in Saturday's assassination attempt at Trump's rally in Butler, PA ... and TMC reportedly bought 50 bullets from a gun store on the morning of the shooting.

Thomas lived with his parents in Bethel Park ... and a neighbor told WPXI the Crooks family had pro-Trump and MAGA yard signs until recently. It's unclear if the seemingly pro-Trump affiliation applied to Thomas himself -- but on its face, it sounds like his parents liked DT.

The shooter's ex-classmates say he was nicknamed "school shooter" and would get bullied in class ... and he was such a poor shot he couldn't even make his school's rifle team.