A week has passed since J.J. Vicari huddled underneath a desk while gunshots exploded in the classroom next door. Now, he is thinking about guns. Not about tightening gun laws, as President Obama urged after nine people were killed at the community college here. But about buying one for himself. “It’s opened my eyes,” said Mr. Vicari, 19. “I want to have a gun in the house to protect myself, to protect the people I’m with. I’m sure I’ll have a normal life and never have to go through anything like this, but I want to be sure.” Mr. Obama...