Bill Clinton was a sex maniac, but that is mostly his wife's business.
JFK was a sex maniac but as far as I know no one complained.
There are plenty of fine examples of ex-presidents who weren't widely accused of infidelity. Nixon, Ford, Carter, Reagan, George Bush, GWB and Obama all seemed loyal husbands to me, far as I remember. I don't remember anyone questioning GWB's fidelity.
Trump seems to be a serial sexual harasser. That's a legal issue.
It usually depends what the guy did whether the press pursues them or not.
That's hardly a history of Democratic bias. I think you are presenting the press history in a paranoid fashion. But then, that is what y'all are told to think every day and so you do.
Does that help?