When Ames Mayfield’s Cub Scout den met with a Colorado state senator last week, the 11-year-old came prepared with a long list of typed-up questions. Ames pressed the Republican state senator, Vicki Marble, on an issue he knew was important to her: gun legislation. The Cub Scout in Broomfield, about 20 miles north of Denver, asked her a slew of questions about previous bills she had sponsored in support of the right to bear arms, and he wasn’t shy about inserting his opinion. “I was shocked that you co-sponsored a bill to allow domestic violence offenders to continue to own...