The U.S. could use a win abroad—something it arguably hasn't had since Osama bin Laden's demise in 2011. Hopes for a peace accord between the Israelis and Palestinians have been dashed, the civil war continues to rage in Syria, chaos engulfs Libya, Russia has invaded Ukraine and China's aggressive behavior in the South China Sea has leaders in Japan and the Philippines drawing analogies to the 1930s.
Amid these storm clouds, Afghanistan is a rare ray of sunshine, and an opportunity.
While the country remains desperately poor and its government much too weak and corrupt, Afghanistan has made striking progress since 2001. U.S. military figures track some of the changes: the miles of road have increased to 26,190 from 11,184; cellphone subscribers are up to 17.5 million from 25,000; the number of schools has increased to 14,034 from 1,000 and there are now 7.9 million primary and secondary students, up from 700,000; and the number of health-care facilities is up to 2,136, serving 85% of the population, from 498 facilities serving 8%.
The April 5 presidential election ratified Afghanistan's progress. More than seven million voters turned out, over 30% of them women, and the two leading vote-getters— Abdullah Abdullah and Ashraf Ghani —are both pro-Western technocrats whose appeal transcended ethnic boundaries. The election campaign, which featured 400 major rallies, was largely free of violence despite Taliban attempts to disrupt the balloting. The Afghan National Security Forces, 370,000 strong, provided secure voting with virtually no coalition help on the ground. Afghanistan is likely to soon see the first peaceful transfer of power in its history.
Ironically, however, the success of the election could spur the White House to slash the number of troops assigned here next year on the erroneous assumption that Afghanistan doesn't need much more help. This risks jeopardizing all of the progress made so far and raises the prospect that Afghanistan could go the way of Iraq. That country was relatively stable when U.S. troops left in 2011. Now violence is back to 2008 levels, and the flag of the Islamic State of Iraq and Syria (as al Qaeda in Iraq is now called) flies over Fallujah.
President Obama risks a similar outcome in Afghanistan if, as recent press leaks suggest, he decides to maintain 5,000 or fewer U.S. troops in Afghanistan next year, instead of the 10,000 requested by the NATO commander, U.S. Marine Gen. Joe Dunford.
That 10,000 figure is itself a bare-bones estimate of what is required—20,000 to 30,000 troops would be a more realistic figure. But U.S. commanders knew there was no chance Mr. Obama would approve such a robust deployment, even though it would greatly enhance the chances of long-term success.
The generals also unwisely attached a timeline to make it more palatable to the White House, promising that all U.S. troops would be out of Afghanistan no later than 2018. This risks repeating the same error as the troop surge of 2010, whose impact was limited by an 18-month timeline which made it impossible to pacify much of the eastern part of the country and which encouraged the Taliban to wait out the offensive. U.S. commanders, moreover, agreed that, in order to limit casualties, U.S. advisers after this year would no longer accompany Afghan troops on missions and the U.S. Air Force would no longer provide close-air-support and medical evacuation to Afghan troops.
But even a time-limited, mission-circumscribed follow-on force of 10,000 could make a critical difference, especially if the U.S. and its allies provide the full $5.1 billion a year in funding the Afghan National Security Forces need to maintain their present strength.
As I heard repeatedly during a visit to Afghanistan last week, Afghan troops are showing growing combat prowess, which allowed them to keep the Taliban from recapturing strongholds in the south last summer. But they still need lots of help with logistics, planning, budgeting, acquisition, high-tech intelligence tools and air power—all sophisticated areas where NATO soldiers remain the essential "enablers." Afghanistan won't have a fully functioning air force until 2017; for providing fire support to troops on the ground, all it has is five Russian-made Mi-35 Hind gunships.
Gen. Dunford's plan would allow Americans to continue working with the Afghans at the six Afghan Army Corps headquarters scattered around the country. But fewer than 10,000 troops would make it impossible for American advisers to maintain a presence at regional hubs such as Kandahar and Jalalabad near the front lines. Instead they would have to consolidate in Kabul where their ability to track and influence battlefield developments in this vast country would be limited. "A number below 10,000 makes the mission here untenable," one U.S. general bluntly told me.
It would be extremely foolish to risk allowing Afghanistan to return to its chaotic pre-9/11 state over a mere matter of 5,000 troops. (At the peak of the U.S. commitment there were 100,000 U.S. troops and even today 33,000 remain.) If Mr. Obama wants a foreign-policy victory in his second term, he will need to puncture this misbegotten trial balloon.
Mr. Boot is a senior fellow at the Council on Foreign Relations and author of "Invisible Armies: An Epic History of Guerrilla Warfare From Ancient Times to the Present" (Liveright, 2014).