It's not about "being polite & non-confrontational" or "taking the high road". It's about avoiding distractions, not being defensive and asserting a confident presidential manner.
He can still "take the battle" to Hillary, but on more substantive issues than a c. 1996 Mis Universe contestant.
This election is Trump's to lose...but he has ceded control of the line of scrimmage to Hillary.
Personally I think Hillary is on the run from the topic because of Trump’s prompt & decisive exposing of the facts. She was all set to have this issue toll Donald like a bell for the next 39 days, now her entire script is up in flames. Her lies can’t stand the light of day & Donald is applying sunlight.