For the second time this month, federal agents have fatally shot someone in Minneapolis while enacting Donald Trump’s crackdown on immigration enforcement.  Alex Pretti did exactly what the National Rifle Association has been telling Americans to do for decades. On a freezing Saturday morning, the 37-year-old ICU nurse at a Veterans Affairs hospital, legally carrying his holstered Sig Sauer pistol with a valid permit, stood between federal immigration agents and a woman they’d just shoved to the ground. He was filming the scene with his phone, one hand raised, when Border Patrol agents pepper-sprayed him, wrestled him down, disarmed him of his holstered weapon and then shot him dead. If there were ever a case that cut to the philosophical core of the Second Amendment as it is preached in conservative America, this is it. The amendment’s legitimacy rests, the right argues, on a single foundational promise: an armed populace is a safeguard against tyranny. Guns are not just for hunting or sport, or even for personal defense. They are the last line between free …