There are a couple of theories of how Australia got an exemption from Donald Trump's steel and aluminum tariffs. The government's preferred narrative is that a century of "mateship" (their word) between Australia and the US and Malcolm Turnbull's close relationship with Trump -- helped by Australia's very own Trump Whisperer, Greg Norman -- secured the exemption.
An alternative is that Trump, they say, is a "transactional president". He's using the threat of tariffs to force Canada and Mexico to agree to changes to NAFTA. He is demanding the EU drops their "horrific barriers and tariffs". And he did a deal with Turnbull: on Twitter, he complimented the Prime Minister for being committed to "a very fair and reciprocal military and trade relationship. Working very quickly on a security agreement so we don’t have to impose steel or aluminum tariffs." Sounds, for all the government's frantic denials that there's any "security agreement", like Trump believes there's a quid pro quo for the status quo.