For the past few months, North Korea has been pestering its southern neighbor with seemingly sporadic swarms of balloons ferrying trash. The garbage has fallen on South Korean roads, buildings and cars — more of a nuisance than a major security threat incoming from a nuclear-armed rival.

       But on Wednesday, the rhetorical rubbish landed on the presidential compound in Seoul, delivering what was perhaps the most humiliating of the unwanted loads from the North so far and raising security concerns and questions about whether the situation would devolve.