Since the time of publication of Trump’s referred book, times have changed dramatically.
We have anti-American militants withing the Continental 48, that could and would strike out at anyone that they have chosen to be deserving. This, alone, should be enough for any right-thinking American to become armed, of some kind.
And his gun/hunting enthusiasts sons have had time to 'splain where he was wrong. he was never terrible and now he is getting to be spot-on.