American supporters of gun control are aflame with admiration for New Zealand, whose government needed only six days after a mass shooting to enact a strict new gun law. “See. It’s not that hard,” tweeted Sen. Chris Murphy, D-Conn. “This is what leadership looks like,” marveled Rep. Alexandria Ocasio-Cortez, D-N.Y. It was notable that Prime Minister Jacinda Ardern pushed through a ban on so-called assault weapons with so little opposition. Also notable were the claims about what it will achieve. “Every semi-automatic weapon used in the terrorist attack on Friday will be banned in this country,” she said. The result...