In Somalia—or Afghanistan—Can Insurgent Defections Change a War’s Course?

Mukhtar Robow, after all, was among the most notorious leaders of Somalia’s al Qaeda affiliate. Luring senior insurgents like him to switch sides is a major war aim for the Western-backed Somali government—and for the U.S. military, which has deployed more than 500 American troops to fight al-Shabaab.

“Defections in general, including by Robow, show that the government’s strategy is working, that people are realizing that this government is the best hope for Somalia,” Prime Minister Hassan Ali Khayre said in an interview this week. “It shows that the Shabaab are weakened and are being defeated—not only militarily but politically, economically, judicially and ideologically, and that public support is on the side of the government.”

Yet, though a few dozen al-Shabaab fighters joined the government since Mr. Robow’s August defection, and despite frequent U.S. airstrikes, the tide of war has hardly turned. Al-Shabaab, which continues to dominate much of rural central and southern Somalia, carried out Africa’s deadliest bombing two months after Mr. Robow’s surrender, killing more than 500 people in Mogadishu.

The Somali movement—like Afghanistan’s Taliban—still holds sway over one of the world’s largest jihadist footholds.

Last month, al-Shabaab finally broke its silence about Mr. Robow—who, in the Mogadishu hotel appearance, had condemned the group’s ideology as “not in the interest of the religion, people and the country.” Mr. Robow, al-Shabaab retorted, was “deluded” to think the group could be undermined.

The question of whether defections by militants, including senior leaders, really matter has been hotly debated by military commanders, intelligence officials and policy makers ever since the U.S. became embroiled in counterinsurgency campaigns in Afghanistan and Iraq following the 2001 attacks.

The U.S. military’s Africa Command said last year that its policy is “to support Somalia-led efforts to encourage members of al-Shabaab and ISIS to defect and pledge support to the Somali Government.”

A similar effort, deployed for several years at great cost, has proved largely futile in Afghanistan, a conflict that bears many parallels to Somalia.

There, the Taliban insurgency—like al-Shabaab in Somalia—controls a large chunk of the countryside and retains the ability to carry out devastating attacks in the capital city. The fighters who defected to the Afghan government often did so for opportunistic personal reasons and usually didn’t represent forces that the Taliban couldn’t easily replenish.

“There certainly have been some individuals who have been reconciled or reintegrated as a result of that effort,” said Laurel Miller, an expert at Rand Corp. who served as acting U.S. Special Representative for Afghanistan and Pakistan until last June. “But I have never seen any indications that one can draw a line between any results that have been achieved via that effort and any fluctuation in the conflict on the battlefield.”

In Somalia, Mr. Robow’s defection quickly proved controversial. In his home South West state, where much of the countryside is under al-Shabaab control, officials embraced the former militant as a potential savior. “Mukhtar Robow is a very good tool. He can reach out to the young people because he knows their language,” said Ali Ali, the state president’s chief of staff.

But many other Somalis—especially those whose friends and relatives had been killed by al-Shabaab when Mr. Robow helped lead the group—were dispirited.

“It’s as if bin Laden was suddenly named a minister or security chief. It’s not a good thing when we give such credit to those who have killed innocent people,” said a Somali lawmaker—who, like several other such critics, feared retribution for speaking out against Mr. Robow in public. Mr. Robow himself couldn’t be reached.

Such anger over al-Shabaab’s atrocities means that, so far at least, there is no effort to negotiate an end to the conflict between the Somali government and the militant group. That is a contrast to Afghanistan, where—despite the Taliban’s murderous record—the central government and the U.S. have been pursuing negotiations with Taliban leaders about a possible political settlement for several years.

Asked about a possible diplomatic engagement with al-Shabaab, Mr. Khayre, the prime minister, suggested that wouldn’t be necessary.

“I see now that my government is winning this war, and it’s just a question of time,” he said.

What is really needed, he added, is greater international assistance to the Somali government, especially by writing off its debt and resuming access to international financial institutions.

Many Western officials disagree with such optimistic assessments of the campaign, and say that—at some point—talking to al-Shabaab may become a necessity, in part because al-Shabaab is mostly a homegrown movement deeply rooted in the country’s clan politics.

“It suits both al Qaeda and al-Shabaab to say they are associated with each other, but actually al-Shabaab is primarily a Somali phenomenon. Very few foreigners have any positions of authority,” said Michael Keating, the head of the United Nations Assistance Mission in Somalia and a former deputy U.N. representative in Afghanistan.

“I do think there is a scope for communication, if not formal engagement, with al-Shabaab,” Mr. Keating added. “The problem is that al-Shabaab right now seems to be in the hands of those who have a very aggressive approach to advancing their political agenda, and I have seen no indication from their side that they see a political track.”

Write to Yaroslav Trofimov at yaroslav.trofimov@wsj.com