No doubt Trump's motive for asking Australian cooperation in gaining evidence to further his personal conspiracy theory is not befitting of an American president. As far as Australia goes, when faced with the option of saying yes or no to sharing intelligence on any matter there is only one answer they would ever give.
"“While Australia’s former high commissioner to the United Kingdom, the Hon Alexander Downer, is no longer employed by the government, we stand ready to provide you with all the relevant information to support your inquiries.”"
The Mueller investigation is always mentioned, while i think all should remember that the FBI investigation into Trump campaign officials conversations with Russians started back in 2013. Some 3 years before the Papadopoulos - Downer meeting.
As for Trump. Trump has always said the Mueller Report exonerated hem so one could ask why is he concerned about the origin of an investigation which cleared him. Looks to me he is sort of putting a lie to his own position.
It was Plato who said, “He, O men, is the wisest, who like Socrates, knows that his wisdom is in truth worth nothing”