When news broke this week about President Donald Trump having a second, unreported meeting with Russian president Vladimir Putin at the G20 summit in Hamburg on July 7, some wondered what the fuss was all about.

Why can’t two presidents engage one another in conversation when they are attending the same dinner? What is so wrong about that? Well, international summits are not wedding receptions. World leaders do not wander from table to table, making small talk. Summits and the meals accompanying them are highly choreographed and scripted events and for good reason.

Whom US presidents engage and how they engage in settings such as these can have lasting implications for foreign policy and the US’s relationships with allies and adversaries. That is why presidents and cabinet members always follow a set of rules on engaging foreign leaders, rules that Mr Trump recklessly disregarded in his one-hour meeting with Mr Putin.