I saw something like 30-50% married people in America have an affair at some point. When you figure that your typical politician is sleazier than your average person, it's not too surprising.
I'll try and find it but I remember seeing a report that showed those numbers to be much higher.
something like 70% for men and 60% for women. With women climbing fast. Up from 45%
Those probably arent the exact numbers but are damn close from what I remember