Millions of Afghans, determined to shape their own future, defied Taliban threats and voted Thursday in the country’s second-ever presidential elections. That courage deserves to be rewarded with far better governance than Afghans have experienced in the four years since the last presidential vote.

President Obama has rightfully defined success in Afghanistan as essential to America’s struggle against Al Qaeda. He has backed that up with more troops — there are 62,000 now with 6,000 on the way — stronger American military leadership and a more careful use of air power devised to limit civilian casualties.

There is a lot more that must be done. The country’s next president will need the full support of the United States and NATO allies if there...