leven years ago, Democratic state lawmakers faced protests and recalls over their passage of a high-capacity magazine ban and universal background checks for gun buyers in the wake of the Aurora and Sandy Hook mass shootings. The legislation cost two senators their seats, including the Senate president, and a third resigned. The backlash left a scar on Democratic leaders, even as the recalled lawmakers said they had no regrets. For several years, legislators introduced few gun reform bills, and none passed. But that timidity is now long gone — a turnaround attributable to increasing Democratic electoral dominance in Colorado and...