– The U.S.-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 the city of Ghazni, 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 U.S. 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.

Q: What is happening in Ghazni?

A: For months, residents and local officials in Ghazni, a city of about 280,000 people, had warned that the Taliban was surrounding the city and making inroads of control. Taliban fighters were even collecting taxes in some areas. By June, the city was living in fear, with people avoiding large gatherings and assassinations becoming more frequent.

On Aug. 10, more than 1,000 Taliban fighters stormed the city in a predawn assault. Officials claim the Taliban were aided by foreign fighters, including Pakistanis and Chechens, and even some al-Qaida affiliates.

The police were forced to retreat and protect the main government facilities — the governor's office, the police headquarters, the intelligence compound, the main prison — leaving the Taliban assailants to entrench themselves elsewhere. The Afghan defense minister on Monday said about 100 police officers and army soldiers and more than 20 civilians had been killed. He put the number of dead Taliban fighters at about 200.

Q: Why does it matter?

A: The siege of Ghazni is perhaps the most audacious example of a Taliban resurgence that has whittled the gains made after tens of thousands of U.S. troops launched a campaign to oust them from power.

While not the first time Taliban fighters have invaded a major Afghan city in recent years, Ghazni's strategic location is important. Its proximity to Kabul and location on the major highway connecting the capital to the south makes it a vital lifeline.

Rahmatullah Nabil, a former Afghan intelligence chief, said Ghazni also was important because some of its neighboring provinces border the tribal areas of northern Pakistan, where militants have long moved with impunity. Who controls Ghazni also affects how freely the insurgents can move into other parts of the country, Nabil said. Taliban control of Ghazni also raises the possibility that the Taliban eventually could surround Kabul itself.

Q: Is this a sign of Taliban strength or government weakness?

A: In recent years, as Afghan forces have largely taken ownership of the war from U.S. forces, the Taliban have continued to gain territory. In some areas, they have struggled to hold a district or city, but in others they are firmly embedded.

According to the U.S. military, the Afghan government controls just over half the country's nearly 400 districts — about 56 percent. Taliban insurgents control 14 percent, and the rest of the country is contested.

A major deterrent to further Taliban gains has been U.S. and Afghan airstrikes. The U.S. military alone has dropped more than 3,000 bombs in the first six months of this year. But air power alone is insufficient.

Nabil said the internal political struggles of the Afghan government and its inability to outthink the Taliban's moves before insurgents invaded a city were underlying problems. He likened the Ghazni battle to the 2015 siege of Kunduz, when it took more than two weeks for government-backed forces to retake the city.

"It was like this in Kunduz also — they first went after the outlying districts, then military bases, and eventually they made it to the city," Nabil said. "Once the city is totally surrounded, entering inside the city becomes easy."