Just over a month after the abrupt regime change in Afghanistan, Iran is still weighing its options on how to deal with the new developments next door. On the one hand, senior Iranian officials have portrayed the US withdrawal as a sign of declining American hegemony. On the other hand, they have been cautious not to allow their stance toward the US to be seen as recognition of Taliban rule.

Beyond Afghanistan’s geopolitical importance as Iran’s immediate neighbor, what affects Tehran’s calculations about the Taliban’s rise are the implications it may have for Iran’s interests in other parts of the region—including Iraq and Syria. In other words, when it comes to Iran’s interests and considerations, the Iranian perception is that what happens in Afghanistan will not stay in Afghanistan....