The US and its nit-witted NATO allies should pack up and leave Afghanistan right now — right here and now.
And this terrible incident might be a major culprit (among a shitload of others).
From the Washington Post on Monday:

An Afghan border police officer opened fire on U.S. troops during a training mission in eastern Afghanistan on Monday, killing six of them in one of the worst such attacks in the past year, according to Afghan and NATO officials.
..
A senior police official said the shooter had been recruited into the border police two years ago.
“I think the Taliban has worked on him,” the official said.
The Taliban issued a statement praising the police officer, whom the group identified as Izzatullah, for the killings.
The group said the man “joined the police force of stooge regime in pursuit of an opportunity to eliminate any number of U.S.-NATO invaders until he got one today.”

This was at least the fifth time in 13 months that supposedly trustworthy Afghan soldiers or police officers have turned their weapons on their NATO partners, and earlier this month, two US GIs were killed in a extreme-similar situation.
Last August, two troops from Spain and their interpreter were killed by another Afghan police trainee, that one a so-called ‘Taliban agent.’
Next to the incident with US troops on Monday, the worse case was in November 2009 when five British soldiers were killed by a rogue soldier as they relaxed on a roof at an Afghan-British checkpoint.

No winning for losing — Pull the plug!