Actually to draw and giving the attacker a second or two to change his mind in my opinion will help you legally. If I can honestly say I presented my firearm to the suspect and told him to stop and even with a gun pointed at him he still charged at me I had no choice he was going to kill me he didn't even care I had a gun.
"The threat was so immediate, I didn't have time to offer the attacker a moment to surrender, nor was I trained to do that."