Lehigh Valley union members are standing up for Democratic nominee Bob Brooks after Rep. Ryan Mackenzie (R-Lehigh) attacked Brooks’ background as a labor leader at the Carbon County GOP Summer Picnic on Tuesday. Brooks, a political newcomer, spent 20 years working as a firefighter in Bethlehem and is president of the Pennsylvania Professional Fire Fighters Association, which represents more than 8,000 firefighters and first responders throughou…