The behavior that goes right up to the line but doesn't cross it, is the complicating issue - I agree. In the case of Donald Trump, there were also a number of depositions filed against him for acts that did break the law, but never saw a day in court.
In most work environments those behaviors would be handled by Human Resources. I understand the process would be complaints submitted, and then a meeting between the accuser, accused, and the HR representative to sort it out to come to a resolution. Most cases are not appropriately handled through national media when it is in that grey area. Work places can have their guidelines for ethics focused on behaviors and then when it comes into question it is accounted for in an HR meeting with a goal of correcting the issue in some manner.
The Donald Trump scenario also introduces a different sort of evidence besides physical evidence, and that is confession. That places it on a different level than someone supposing him to look at their body. He stated his intention, so it is a form of evidence. I don't know he could be imprisoned for that alone. I see it as motivation to do comprehensive FBI level investigation because it implies that legal lines could have been crossed. People who dismissed it as locker room talk are as absurd as the people who call a social pat on the back at a cocktail party sexual harassment.
So much human behavior goes right up to the line. I had the opportunity to watch women do the same thing when I knew a man with an image of being a local 'rock star' sort. Women were very overt in the physical posturing socially. I had no idea women were that aggressive sexually. This man also told me that his high school English teacher was hitting on him and sexually harassing him. I believe him because I saw so many women toy with the boundaries with him. Edit: The high school English teacher's behavior should have been stopped with potential legal repercussions. /edit Still with most of it, there isn't much that can be done when motivations cannot be defined definitively. I'm not a fan of the behavior and it's one reason I avoid a lot of social interactions, but my concern is litigating so much grey area making the world a huge pile of eggshells for people to walk on. There are so many behaviors that are violating, but left with plausible deniability. I don't have a complete answer because it would be great if that stopped, but I don't see an ethical way to force it to stop. I think you have to live with some degree of annoying, intrusive behaviors from people.