Yup, polls can't account for something like an "October surprise". In Hillary's case in 2016, that was the James Comey letter that was leaked by Republicans Congress. It had the desired effect, with her poll numbers dropping virtually overnight. He rescinded the letter, but not fast enough to make a difference. This was all prompted by FBI agents in the NYC office who were leaking like a sieve to the press. So if you ever hear someone grouse about prosecutors supposedly interfering with elections because they are prosecuting Trump for his crimes, remind them that Trump got a whole presidential term out of FBI agents interfering for him.