How social media's intersection with politics has created a situation akin to war.
Hundreds In Arizona Gather To Honor Murdered Border Agent
They were here to honor an elite Border Patrol agent murdered last month. Brian Terry was a former Marine and cop who became an agent in his late thirties.
Agent Jose Verdugo had known Terry since their days in the Border Patrol Academy.
They they ran into each other in a hall recently and Verdugo says he wasn't surprised to see Terry in the uniform of the Border Patrol Tactical Unit.
"Brian, your work ethic, your integrity and your sense of honor were infectious and inspirational. Rest in peace, super-cop," he said.
"The reason why he was in those canyons west of Nogales and the reasons why our Border Patrol agents go out on the line and stand between harm and the American people is because we are determined to restore the rule of law to the United States Mexico border. And this sector in Tucson is the last place where it must happen," Bersin said.
Four Mexican men have been arrested as part of the investigation into the murder. Nobody has been charged.