Also, lets say you use lethal force in your home when a perp breaks in. Are they going to drug test you and if you had THC in your system could that negate your rights? The more I think about it this it is going open a huge can of worms.
I would say most likely not, without probably cause. If the police investigate and smell pot, or see the bong you left out, or whatever, they certainly might. Then again, it's going to be investigated by state or local police who, in their jurisdiction, pot is legal. So, who knows?
Not getting into whether pot itself is good or bad, or whatever, but given that being a user of a controlled substance make you a prohibited user, according to the Feds, and pot is a controlled substance according to the Feds, it probably a good idea to pick the one you think is more important in your life, pot or guns.