TACTICAL BASE GAMBERI, Afghanistan — Lt. Gen. Mohammad Zaman Waziri had an immediate question about the possibility that President Trump would send more American troops to Afghanistan.

“Are there going to be only advisers?” he asked an American delegation visiting his base in heavily contested Nangarhar Province on Monday.

His question cut to the heart of the line that the Pentagon is trying to straddle in the war against the Taliban, who are gaining ground and now control more territory in Afghanistan than they have since an American invasion ousted them from power nearly 16 years ago.

The war has become more widespread, violent and complex than ever. Mr. Trump, in an address on Monday night, promised a renewed American military commitment to Afghanistan, but did not offer specifics such as how many more troops might be sent there. The Pentagon had requested 3,900 additional troops.