Turnbull should strive to be "not too hot" and "not too cold." He needs to be "just right" in his interactions with a president who is by far America's most unpopular relative to his peers after one year in the job.
After 18 months of investigations, there is no email or document or witness's testimony that proves Russia-Trump collusion. In short, there is still no smoking gun.
Barack Obama wanted three attributes of Australia for America. He wanted Australia's universal healthcare system, its gun laws and its compulsory voting system. These are three of the defining differences between the two societies.
Turnbull can't choose not to engage with Trump, nor can he choose never to differ with him. No relationship works like that, and certainly not one where aligned, but markedly different national interests are at stake.