"Supersonic Crack: This sharp, whip-like sound is the first thing heard. It is created by the shockwave produced as the bullet travels at supersonic speeds, breaking the sound barrier."
This is correct, but the bullet only breaks the sound barrier once, and that is as it exits the barrel.
Once the bullet exits the barrel, it immediately starts slowing down. It is still travelling at supersonic speed, but it does not break the sound barrier a second time. It passes the sound barrier as it slows, but that passing does not makes any noise.
The bullet nicked/grazed Trump's ear and apparently, did not do any significant damage. Why this is controversial is beyond me.