Um. Yes?
I'm not sure why you think running for office is some sort of magical process that transformed Trump into a new being, all old sins forgotten. Men in power cheating on their wives is a tale as old as time, and isn't significantly changed depending on where that power derives. Unless Bill had pulled a Petraus and leaked state secrets, which he didn't, it was a failing of the man, not the office. I recall that we were pretty bored by the whole thing before the GOP was.
But as you say, attacking Hillary for what Bill did isn't kosher, and Trump's house is extremely glassy in that respect.