The summits are not endpoints. They are the mechanism by which two countries, which can neither resolve their differences nor afford to rupture them, manage the interval between crises.
Trump and his advisers have repeatedly insisted that the U.S. president can pretty much do whatever he wants and that the pesky Congress need only be consulted rarely.
When political legitimacy becomes contingent on recognition by a superpower, populations lose their right to self-determination and democracy becomes a selective tool.