The TV mini-series Diversant [The Saboteur, Andrei Maliukov 2004]
depicts the rigorous training of young soldiers to transform them into
professional saboteurs.1
"Who knows?" is an example of a rhetorical question, because it is really a statement that does not actually ask for an answer.
The consensus is that it's sometimes OK to skip question marks for rhetorical question. Some people will say you shouldn't ever skip a question mark for a rhetorical question, and no one minds if you use a question mark, so I suggest that you do. (Personally, rhetorical questions without question marks always throw me off -- John Grisham has a habit of doing this and it causes me to read these sentences in a weird, sarcastic tone)
Depending on the context, a rhetorical question may be punctuated by a
question mark (?), full stop (.), or exclamation mark (!),[6] but some
sources argue that it is best to use a question mark for any question,
rhetorical or not.[7]
According to Wiktionary (I think it has the best definition), the adjective go-to means:
Desired; desirable; of choice: 'Cheesecake is my go-to food whenever
I feel down.'
Reliable; likely to perform in difficult circumstances: 'Smith is your go-to person if you want lasting results'.
Your example sentence could be rephrased to:
... his typical arguments on which he always relies or that
we could always expect him to make whenever he find someone (talk
show hosts, journalist, pundits and political consultants) to
attack for why someone is a loser, a dope or a dummy is that he or
she has made erroneous predictions...
Those arguments are typical of Donald Trump and he uses them so frequently that they are arguments of choice or preferred above others by Donald Trump.
Best Answer
This is a transliteration of the Russian word диверсант, which means saboteur. From Cinepaternity: Fathers and Sons in Soviet and Post-Soviet Film by Helena Goscilo, Yana Hashamova: