KABUL, Afghanistan — The American-led invasion of Afghanistan routed Taliban extremists from power after the terrorist attacks of Sept. 11, 2001. Nearly 17 years later, after tens of thousands of deaths, hundreds of billions of dollars spent and two White House administrations come and gone, those extremists are not only undefeated but seem as strong as ever.

Since Friday, Taliban fighters have roamed the streets of Ghazni City, a strategic urban center less than 100 miles from the capital, Kabul, killing dozens of Afghan soldiers and police officers, cutting communications and severing the main highway from Kabul to the south and beyond.

The Ghazni assault has demonstrated a stunning display of Taliban tenacity that belies the official Afghan and American narrative of progress in the war and the possibility for peace talks. It also has revealed remarkable bumbling by the Afghan military, including the wrong kind of ammunition sent to besieged police officers. Moreover, the siege has raised basic questions about what conditions the Taliban might accept for peace talks.