When Donald Trump welcomes the Group of 20 to his private golf resort in Miami next year, he'll decide who's on the guest list. That much is clear after the US president said in a social media post Wednesday that he won't invite South Africa, the holder of this year's G-20 presidency and the object of the US president's ire for some time now. It may be a breach of long-established protocol for a leader to decide which of the bloc's members can attend the summit " let alone to host the event at their own hotel " but Trump has demonstrated that he cares little for either convention or the multilateral order.