On Monday night, President Trump recommitted the United States to the war in Afghanistan, saying that the U.S. military must “fight to win.” Acknowledging the fatigue many Americans feel after almost 16 years of war in the Middle East and South Asia, Mr. Trump conceded that his own instinct was initially to pull out the troops. As a candidate and private citizen, Donald Trump favored withdrawal, tweeting in 2013 “Let’s get out of Afghanistan.”

After more than a decade of fighting has failed to bring victory and peace, the majority of Americans say the war was a mistake. Young Americans who could soon be deployed may not remember the attacks of Sept. 11, 2001. Nevertheless, after a months-long strategy review, Mr. Trump is reaffirming and expanding our commitment to the war in Afghanistan. In his speech, Mr. Trump claimed the responsibilities of his office have led him to change his mind. I interviewed Drew Christiansen, S.J., the distinguished professor of ethics and global development at Georgetown University, an expert in just war theory, and former editor in chief of America, for his insights on the latest developments in the United States’ longest war. The questions and answers have been edited for brevity and clarity.

Is the war in Afghanistan defendable under just war theory?

The war in Afghanistan is defendable under just war theory. Pope John Paul II in 2002 made that clear, that defense against terrorism is part of the state’s right to self-defense. Of course, you have to take into account the suffering the war inflicts and ask: Does our effort, which has gone on for so many years now, begin to be disproportionate and to cause undue suffering? That’s a very hard question to answer.

What are your expectations for the success of President Trump’s new approach?

I think there is not much expectation for drastically different success. We will likely see some modest improvements in the situation. There are just so many terror groups embedded in Afghanistan—you have the Taliban, the Haqqani network and now, of course, ISIS, which we are fighting on multiple fronts. The truth is that the Afghan troops, despite years of training and funding, are still not capable of maintaining or imposing order themselves, and that situation isn’t likely to change anytime soon. Nor is the United States going to occupy the entire country; it simply isn’t willing to. Some people may be sanguine about the prospect of success, but most serious analysts are not.

This is a place that has defeated most invaders; the Russians didn’t win. We’re in a stalemate.

Of course, despite the death and destruction the war there brings, Afghanistan has been a proven base for terror activity. The United States does have a right to self-defense and a right to be worried about the resurgence of many of these terror groups, but for now, it seems we are simply in a holding pattern. Obama and Trump both made this mistake, focusing too much on the killing and not putting enough money and attention into civilian and diplomatic efforts, efforts at development. Obama didn’t emphasize those enough, while Trump appears to be cutting those altogether, which is very bad judgment. Tribal societies are very difficult to pacify and unless we can make progress at that level we are in a military stalemate. This is a place that has defeated most invaders; the Russians didn’t win. We’re in a stalemate.

President Trump directly pledged an end to “nation building.” What do you make of that?

It is very single-minded. The truth is the United States never invested enough in nation building. Trump is exaggerating the mistakes of the past. Obama left most of our development efforts underfunded. The focus on killing will take a toll on Afghan society.

Is Mr. Trump’s approach then trading the safety of Afghan people for our own?

Well, we are not fighting the Afghan people; we are fighting terrorism. Most of the damage on Afghan people has been inflicted by the Taliban. But, of course, a policy of nation building says we are committed to the Afghan people. We have a right to self-defense but also a responsibility to mitigate the greater injustices that might be done otherwise.

We are not fighting the Afghan people; we are fighting terrorism.

What does the difficulty Afghans have experienced coming to the United States, notably the case of the Afghan girls’ robotics team, say about the United States’ goals in the region?

Well, first off, we do have to acknowledge that there is historically a real problem of terrorism being exported through Afghanistan. There is a quite stringent vetting process for anyone traveling from Afghanistan to the United States. Nevertheless, there should always be flexibility in cases like the one you refer to. Those kinds of diplomatic and cultural exchanges and the opportunity for Afghans to travel to the United States could become long-term building blocks for peace—peace through exchange. 

As President Trump alluded to in his address on Afghanistan, the nation is experiencing deep divisions over race and other issues. How does Mr. Trump’s call to unify the country in wartime affect this, and how do Americans who are increasingly against the war respond to this call?

Well this is the underlying problem of a democracy at war. It is hard for the people to stay focused on the war. You simply can’t win this kind of war, a counterinsurgency, on the timescale of election cycles.

In regard to the specific timing, after Charlottesville, yes I think the president was glad to have an opportunity to change the subject, but this decision was due anyway. Afghanistan has been an issue for a long time and the announcement of a decision was due.

The American people are understandably tired of this war that has gone on for so long, longer than any other in our history. But at the same time, most people understand the need to do something about three major groups committed to exporting terror. If you ask the question that way instead of just “should we be there,” I expect you will find the American people more supportive of our commitment. The question a lot of people have is can we win? The war so far has never been wisely handled, and Americans are right to be tired of that. But the approach that we’ve taken, that Trump appears to be augmenting, is wrongheaded. Killing and nothing else is wrongheaded and has no hope of succeeding. Killing to the exclusion of development is doomed to failure; you need to win the Afghan people’s support; you need it to deny hospitality and support to the insurgency.

Antonio De Loera-Brust is the communications director for the United Farm Workers. He previously served as special assistant to U.S. Secretary of State Antony Blinken. He was an O’Hare fellow at America Media from 2017 to 2018.