That's a valid question, mama cass. I honestly don't know, other than it's likely party loyalty/hatred playing out. If you hate Trump, of course you're going to support Stormy, if you like him, you're going to think she's lying. Same thing applies to everything with Clinton and Monica.
And I think some of it is the fact that the world was a different place in the '90s than it is now, and attitudes on these situations will continue to evolve and change with time. Not that that excuses or justifies the attacks and insults made towards Monica, of course, just that that sadly likely explains some of the difference in reactions as well. I think Monica would have an easier time getting sympathy and support today, though, thankfully.
I never care about a politician's affairs, regardless of their party. That's for them, the person they cheated with, and their families to sort out, it has no impact on my life one way or another (though I obviously think a president should spend more time focusing on handling serious matters than trying to hook up with people). The only time it ever bugs me is if said politician is having affairs while also going around harping on about how we need to "protect the sanctity of marriage" by not letting gay people get married and other bullshit of that sort. But it's not the affair itself that's the problem there, it's, obviously, the hypocrisy.