 July 4th is just around the corner. The holiday period has seen an uptick in mass shootings in recent years for several reasons. Gun violence experts blame the uptick on a combination of factors. More gatherings, hotter weather, but also greater anger and access to weapons. There have been a total of 80 mass shootings in the U.S. over the last three years, from July 1st through July 7th. A mass shooting is defined as one that kills or injures four people. ABC's Brian Clark on the shootings.