As you say, we don’t yet know. It’s worthless to speculate the background and motives of the shooter, but it makes zero sense for this to be a politically motivated assassination by a conservative. My personal gut feeling is this was a politically motivated attack from the left. Time will tell.
A 200 yard shot with a rifle is not a hard thing to do. I’m not a firearms instructor, but I’m confident I could train someone completely novice to firearms to hit a man sized target at 200 yards with iron sights in 1 hour at the range.