MEXICO CITY — It's one of the safest parts of America, and it's getting safer. It's the U.S.-Mexico border, and even as politicians say more federal troops are needed to fight rising violence, government data obtained by The Associated Press show it actually isn't so dangerous after all. The top four big cities in America with the lowest rates of violent crime are all in border states: San Diego, Phoenix, El Paso and Austin, according to a new FBI report.