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.
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.