CONCORD, N.H. — Gov. Chris Sununu on Friday vetoed three bills that advocates said would have added “commonsense” protections for Granite Staters against gun violence but opponents said would have done nothing to stop mass shootings and would have infringed on the constitutional rights of citizens. Sununu vetoed House 109, which closes the so-called gun show loophole and requires background checks for virtually all commercial firearms sales or transfers; House Bill 514, which requires a three-day waiting period before the purchase and delivery of a firearm; and House Bill 564, which prohibits carrying a firearm on school property. “New Hampshire...