Eric Trump is furious with the security lapses leading up to the assassination attempt on his father ... and says a competent shooter wouldn't have missed his target.

Donald Trump's son expanded on his father's brush with death in an interview with "CBS Evening News" anchor Norah O'Donnell ... saying it's hard to believe Thomas Matthew Crooks was able to fire at the former president from close range.

Eric says he grew up competing in shooting sports and a "rifle shot from 130 yards is like a four-inch putt ... you don't miss it if you're competent." A golf analogy for the Trumps is pretty on brand.

ET also finds it hard to believe the U.S. Secret Service seemingly overlooked the large building where Crooks scaled the roof and took up a shooting position ... saying it doesn't take a security expert to realize that's a place that must be secured.

Of course, Trump turned his head as the bullet flew by ... something he says President Joe Biden even asked him about ... and he's been walking around the RNC with a bandage on his ear.

Eric gave a separate interview with "CBS Mornings" where he said his father didn't need stitches but had a nice flesh wound and a massive earache.

All things considered, Donald's son says someone must have been watching down on his father because things "could have gone very, very differently."