Good question. I don’t remember any ambush attacks at police under other presidents. It was usually a suspect with nothing to loose gets pulled over, not going out to find and kill cops.
Black were shooting cops in the 1960s and 1970s, though these ambushes are being encouraged by the POTUS. THAT is what is making this so dangerous, IMO.
Ambush attacks in the early 70s by groups like the black panthers were rare but happened.