Americans increasingly favor tougher laws, but they also say change is unlikely to happen anytime soon, a survey shows.
The teenager suspected of killing nine people was obsessed with mass shootings and apparently acted alone, officials say.
A gunman kills at least nine people and injures many more at a shopping center before killing himself.
Senator Tim Kaine of Virginia emerged as a leading contender in a field that also included Tom Vilsack and Thomas Perez.
The presumptive Democratic nominee says the GOP convention was "dark" and isolationist.
The Summer Olympics host city has seen a sharp increase in violence, including scores of police killings.