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.

Now, questions over who will and who won’t go are starting to pile up, not least over which nation might make up the numbers. The move puts other G-20 members in a bind: ignore the insult and make the trip anyway, or stand in solidarity and risk the full force of a Trump blowback in trade tariffs, technology embargoes or worse.

“This is one of the most important multilateral forums we still have in the world,” and a format that “we should not diminish unnecessarily,” German Chancellor Friedrich Merz said in Berlin on Thursday, when asked about Trump’s comments.