When it’s a Republican. Republicans are held to a standard of 100% purity, while for democrats anything goes, and in fact the more outrageous the dems’ behavior the more it’s defended and celebrated. It’s like Republicans are living in pre-Bill Clinton days, when even a hint of infidelity was instant death to a political career, and dems live solidly in the present, when even the most sick, perverted behavior actually makes them MORE likely to be elected.
That’s because we sell family values. When we don’t live by them, we get called out. Democrats do not have family values in their platform so it doesn’t matter as much.