After all, Donald's group of advisers not always follows its declared motto "Let Trump be Trump". When everyone was expecting a new serving of trolling from Donald, he surprised the public by keeping silence and leaked reports that he strictly prohibited his political team from discussing or commenting on this sensitive issue anywhere at all.
It is important to says that US media, even those supporting Clinton, have been playing the revealing video of Clinton almost nonstop. The picture would reach the majority of voters even without Trump's remarks. While the probability of a blunder would be high.
This is a good example of analytical work in the crisis situation being done not only by the staff of the candidate "who got into a mess" (in this case it was Clinton) but by the competitor staff too. And here they found the perfect answer to the question of "How to react?"
Trump not only avoided a mistake which his opponents would not let go unnoticed, but showed sympathy to the rival, which was the worst of all possible reactions for Clinton in this whole story.