John Hardly,

To the extent that the Democrats are immune from sex "scandals" - if they are - it's because they, as a party, do not tout themselves as "the party of family values" (even though they are more supportive of families on most issues than the Repubs are). They don't run on trying to rid the nation of the scourge of homosexuality. They basically view sexual behavior between consenting adults as a private matter and not the law's business.

It's the Republican party, many of the leaders of which are known adulterers and/or engage in sequential marriage (ofteninvolving trading in the older wife for a new, flashier model) and/or avail themselves of the services of prostitutes, that leaves itself open to such "scandals" by virtue of that holier-than-thou stance on sexual matters.