Since Ahmed Wali Karzai lived like the Tony Montana of Afghanistan, it almost seems inevitable that half-brother of the Afghan president died the way he did.

The man known by the U.S. military as AWK was gunned down in his Kandahar home by one of his own bodyguards, Sardar Mohammad, on Tuesday morning. Very conveniently, other members of the AWK guard force killed Mohammad.

The Taliban are claiming credit for the assassination. But AWK, who ran the Kandahar provincial council, had no shortage of enemies. Deep breath: there’s probably going to be a power struggle in Kandahar now.

AWK was a classic warlord. More powerful than the province’s governor, he had connections to the drug trade, fueled by American largesse, and controlled a fearsome private militia. The U.S. military, alarmed that AWK’s corruption made the Taliban’s argument for it, thought him so dangerous to the war effort that it considered putting him on its “kill or capture” list. Officials at the U.S. embassy in Kabul debated prosecuting him. But AWK reportedly was the CIA’s man in Kandahar — which blunted U.S. moves against him and exposed the incoherence of American anti-corruption strategy.

But AWK also maintained a large patronage network that kept him in power. Last month, Matthieu Aikins of Harper’s reported that a “who’s who of pro-government figures” convened to discuss a push to install him as Kandahar’s governor. AWK paid for the event....