The bathroom issue is just another issue the left wants to focus on in an attempt to drag the GOP candidate into a debate on social issues, which normally spells doom for the GOP. This time, assuming it's Trump, it'll be different. Either way, considering both the number of people actually effected combined with the small likelihood of any incidents; it should be a non issue.
The only actual issue, however minor, is the absence of anew objective standard. Obviously 99% of trans won't go into a bathroom/dressing room to stare. The problem is stopping the other 1%. Without an objective standard defining exactly when someone is trans enough to use whichever facility, it's impossible. Otherwise it has to be decided subjectively on a case by case basis, which sets up tons of litigation.
Come up with an objective standard for trans. Or require people to use the facility that matches their biology. Those are the only 2 logical choices.