In a July, 2016 file photo, Marine Gen. Joseph F. Dunford Jr., right, chairman of the Joint Chiefs of Staff, meets with Army Gen. John W. Nicholson Jr., commander of the Resolute Support mission and U.S. Forces Afghanistan, in Kabul.

KABUL, Afghanistan — For months, Gen. John W. Nicholson, Jr., made the case for an expanded U.S. military commitment to Afghanistan, telling skeptics that the faltering Afghan war was an urgent matter of American security, that the struggling Afghan government was a reliable partner, and that its defense forces just needed more time and U.S. support to become self-sufficient.

Last week, the top U.S. military commander in Afghanistan finally got his wish.

President Donald Trump, who once advocated abandoning Afghanistan and in recent months questioned the fundamental premises of America's costly 16-year military involvement here, has now publicly committed himself to a strategy that hews closely to the military plan Nicholson and Afghan President Ashraf Ghani hammered out in dozens of meetings this spring and summer.

Now, the burden will be on Nicholson, 61, a boyish-looking four-star general who has spent more time in Afghanistan than any other senior commander, to deliver on what many observers say may be an impossible mission. Its aim is to help Afghan forces turn around a stalemated conflict with the aid of a few thousand extra advisory troops — something his predecessors failed to do with more than 100,000 combat troops at the war's peak.

Trump and Nicholson do not know each other, and the general said last week that he communicates with administration officials through the military chain of command, meaning his boss at the U.S. Central Command in Tampa. At one White House meeting to discuss Afghan policy, Trump reportedly threatened to fire the popular Nicholson out of frustration at the stumbling war effort, stunning his aides.

In an interview at his headquarters here Friday, Nicholson declined to discuss that episode, and he referred to Trump's speech on Afghanistan several times rather than answer questions directly. Asked if he now believes the president supports him, Nicholson paused, smiled and answered, "Yes." Asked to elaborate, he smiled again and shook his head.

If he has any doubts about his mission here, the congenial but cautious West Pointer has buried them beneath a can-do persona and a glass-half-full approach to every problem. He exudes confidence in Ghani and his determination to reform the Afghan security forces, which have been weakened by corruption and nepotistic leadership. He heaps praise on the Afghan special operations forces, which will be doubled in size and trained by U.S. and NATO advisers under the new military plan.

And he is relentlessly on message about connecting the dots among the ongoing fight against Afghan insurgents; the dangers of terrorism radiating from an unstable, Taliban-plagued Afghanistan; and the American interests at stake in making sure this impoverished Muslim nation does not again become a redoubt for international Islamist militias such as al-Qaida and the Islamic State.

"As a soldier, the concern I have is about terrorism emanating from this area," Nicholson said in the interview, echoing Trump's speech last Monday on Afghan strategy. "The requirement to keep pressure on these terror groups to prevent another attack on our homeland . . . fundamentally, that is why we are here."

Americans, he added, "need to be concerned about the Islamic State emerging from this region. The Taliban enable them to exist, and if the Taliban were to return, they would flourish." A return to Taliban rule , he said, "would mean another threat to our homeland."

There is also another more personal aspect to Nicholson's commitment: an evident empathy for Afghans and their struggles, developed through four tours of duty totaling five years of immersion in the conflict — from early optimistic days of sipping tea with tribal elders and inaugurating village projects to later struggles with military setbacks and growing Afghan resentment of the foreign military presence.

"I believe in the Afghan people," he said. Since his first assignment here in 2006, he continued, "I came to have great respect and affection for the Afghan people, who have endured an incredible amount of hardship for the last four decades, yet still in spite of all that are incredibly pious, hard-working, hospitable and truly want a better life for their children."

That attachment deepened during one of the worst crises of the U.S. combat mission, when an airstrike on a Doctors Without Borders hospital killed 42 people in 2015 during a chaotic battle with Taliban forces in the northern city of Kunduz. Several months later, when Nicholson assumed command of the U.S. reduced advisory mission, a U.S. military report came out acknowledging that a series of errors had led to the tragedy. Nicholson immediately apologized to the nation, then flew to Kunduz with his wife and met with families of the victims.

"It was a very emotional and personal event," he said. Afghans "don't want to see a return of Taliban rule, and they genuinely appreciate our help. So when we make a mistake, it is the right thing to do to reach out to them." The gesture also had a strategic aspect. "In this culture, when you make a mistake and make a genuine apology," Nicholson said, it is "almost always accepted, and you are able to move on in the relationship. . . . That needs to happen in this long war."

Lately, Nicholson said he has spent a lot of time consulting with Afghans of all political stripes and affiliations, seeking support and common cause at a time of domestic political turmoil and uncertainty about U.S. intentions, especially with the post of U.S. ambassador vacant since last winter. As a matter of course, he works with senior army, police and intelligence officials.

But the Afghan closest to Nicholson is Ghani, a no-nonsense technocrat who is often criticized by Afghans as autocratic and remote. The general, who meets with Ghani several times a week, called him a "very willing and capable partner" who is pursuing "rigorous reforms" across the government and the security sector, where corruption and poor leadership have been major impediments to the war effort.

Nicholson particularly praised Ghani for replacing a number of senior army and police officials with others who were more qualified and not tainted by corruption. He pointed to the removal of two army commanders in Kandahar and Helmand provinces, one of whom was recently convicted of keeping money for soldiers' food and using combat troops as personal guards. Their replacements, he said, have "fundamentally changed the environment. . . we're already seeing a difference on the battlefield."

The general declined to discuss Pakistan's role in the Afghan conflict, although for months he publicly argued in Congress and elsewhere that Pakistan was harboring Taliban fighters and that the U.S. government should pressure Pakistan to stop. In the interview, he was far more circumspect, referring vaguely to the problem of "external enablement" of insurgencies but stating that relations under the new U.S. strategy will be "managed from Washington to Islamabad."

Nicholson was much more loquacious about the challenges on his own turf, with a ready list of achievements he hopes the expanded U.S. role in Afghanistan will produce. They include the defeat of al-Qaida and the Islamic State, the reduction of foreign support to the insurgents, the increased capacity of the Afghan security forces, and the "marginalization" of the Taliban insurgents until they must either "die or reconcile." Reconciliation will be complicated, he acknowledged, "but this conversation needs to begin."

