This question is about getting out of the US by land.
Has anyone with a valid destination visa/visafreevisa-free ever been refused land entry into Canada/Mexico?
It appears that border guards can refuse people entry at the border for whatever discretionary/discriminatory reason. In that case, what happens next? Do you simply get returned to the US? But you no longer have a valid visa/estaESTA, nor can you apply for one.
Also, physically speaking (take for example, leaving a sanctuary state by Amtrak into another country), do you exit US customs before entering the next country's? Or are they one-and-the-same with no physical "limbo" space?