For the U.S. and its NATO allies, Afghan President Hamid Karzai has been a frustrating friend. His calling for the withdrawal of the foreign troops that are fighting to preserve his government and saying on one occasion that he might join the Taliban are indefensible.

Karzai’s tendency to believe that he faces unseen enemies has probably been exacerbated by the death this week of his half-brother Ahmad Wali Karzai. Yet, with President Barack Obama committed to reducing the U.S. presence in Afghanistan, finding a way to work with Karzai is critical to preventing Afghanistan from again becoming a sanctuary for al-Qaeda and other terrorist groups. The arrival of a new American team in Kabul provides an opportunity for Obama to reset his relationship with Karzai. We encourage him to do so.

The new team is led by people with excellent reputations: Ryan Crocker, who won accolades for his work as ambassador to Iraq; Lieutenant General John Allen, who will command of NATO’s military forces; and Marc Grossman, who succeeds the late Richard Holbrooke as Obama’s top Washington-based diplomat on Afghanistan. They are likely to find that working with Karzai tests their interpersonal skills.

A Personal Hit

The assassination of Karzai’s half-brother will probably have a profound personal effect on the Afghan president. The two men were personally close, and Hamid Karzai relied on Ahmad Wali Karzai to manage the complicated tribal politics of the volatile Kandahar region. Although members of the Taliban have claimed that one of their sleeper agents killed him, it appears more likely that a trusted associate turned against him for personal reasons. This will probably confirm Hamid Karzai’s view that he is besieged by enemies on all sides and can’t rely on anyone, including his American partners.

Karzai’s distrust of the Obama administration is exacerbated by his conviction, right or wrong, that Obama has sought to undermine him or even remove him from office. Crocker, Allen and Grossman will have to go out of their way to reassure Karzai of U.S. support. In doing so they should emulate Zalmay Khalilizad, the former U.S. ambassador to Afghanistan, and General Stanley McChrystal, the former NATO commander there, who enjoyed excellent relationships with Karzai. Both Khalilizad and McChrystal went out of their way to publically praise him and treat him as a head of state, even while delivering tougher messages in private.

Echoes of History

Ahmad Wali Karzai’s killing comes on the heels of Obama’s decision to begin a substantial withdrawal of U.S. forces this year, and to remove all combat forces by the end of 2014. Hamid Karzai undoubtedly views this decision as a sign that the Americans plan to abandon Afghanistan to its fate, now that the threat from al-Qaeda seems so diminished. Like most Afghans, Karzai remembers how, after a decade of supporting the anti-Soviet insurgents in the 1980s, the Americans lost interest as soon as the Soviets withdrew, condemning Afghanistan to years of chaos and the rise of the Taliban.

The perception that Washington is about to wash its hands of Afghanistan might tempt Karzai to try to cut the best deal he can with the Taliban and Pakistan or, failing that, to turn to Iran for support. It would be disastrous if America’s more than 10-year commitment to Afghanistan ends with Tehran or Islamabad as Kabul’s most influential foreign partner.

To boost Karzai’s confidence and strengthen his negotiating hand with the Taliban, Obama should reiterate his interest in a long-term strategic partnership with Afghanistan, including a commitment to keep trainers and other support troops there after 2014. The Americans will leave behind the largest and best trained military in Afghanistan’s history, but for the foreseeable future the Afghan economy will be too weak to finance it. Obama can resolve this problem by committing the U.S. and its allies to pay for the Afghan security forces until the government is no longer threatened by extremists.

Obama should also try to develop a personal rapport with Karzai, as President George W. Bush did. If Obama wants to salvage success from his Afghan policy he will have to work the Karzai account hard, and should initiate a regular series of personal contact.

Karzai is an exasperating and often infuriating ally. But we are passing through a delicate moment, and it would be better for the United States and the world if Obama had Karzai working with him rather than at cross-purposes.

Read more Bloomberg View editorials.

To contact the Bloomberg View editorial board: view@bloomberg.net.