Here is President Barack Obama, on June 22, 2011, announcing the withdrawal of 33,000 troops from Afghanistan: “America, it is time to focus on nation-building here at home.” And here is President Trump on Monday, announcing the dispatch of more troops to Afghanistan: “We are not nation-building again. We are killing terrorists.”

But when I visited Afghanistan a few days ago, traveling with Gen. Joseph L. Votel, the chief of the United States Central Command, all the briefings I received from American officials were about nation-building. Admittedly, no one used that term — the preferred euphemisms are “capacity building,” “enabling” and “working by, through and with.” But the intent is the same: to create Afghan government institutions that can overcome the threats from the Taliban, the Haqqani network, the Islamic State, Al Qaeda and other Islamist terrorist groups active in that country.

The United States really has no alternatives. It is willing neither to abandon Afghanistan, that way allowing it once again to become a safe haven for transnational terrorists, nor to put the entire combat mission on the backs of United States forces, an effort that would call for the deployment of hundreds of thousands of troops.

Some, like former Vice President Joseph R. Biden Jr., have argued for a narrowly focused counterterrorist mission with a small number of Special Operations forces. But that model was discredited by recent history in Yemen, where the collapse of the central government forced the withdrawal of American Special Operations forces. No counterterrorist operation can be effective in a chaotic and lawless environment where insurgents control a significant proportion of the country.

The only conceivable path to success lies in fostering stable and effective institutions of government that can police their own territory with diminishing amounts of outside assistance. In other words, nation-building.