The US spend 20 years in Afgan fighting to remove the Taliban from power only to hand power to the Taliban.

The US spent years fighting north Vietnamese forces only to sign a peace treaty, leave south Vietnam and then 2 years later have North Vietnam take over South Vietnam and unify the country.

You don't consider completely failing your objectives failure?

Saigon fell, and the Taliban regained control of Afghanistan.

Definitions of "lose" have been updated by firesteelrain to exclude retreating after failing to achieve anything.

Who rules Vietnam? Who rules Afghanistan? Tell us.