But there are new claims that U.S.-funded contractors have been spending a hefty chunk of that funding on protection payments to the Taliban - for years, reports CBS News correspondent Nancy Cordes.
"That translates into money that the Taliban are using to attack and kill American military personnel, and that's just simply outrageous," said Rep. Bill Delahunt.
The international news organization GlobalPost quoted several unnamed contractors who said 20 percent of their budgets - or more - go to pay off the Taliban so it won't bomb their projects, or their people. It's a protection racket far more sophisticated than the typical mob-style shakedown.
"The Taliban literally has an office in Kabul where it works out what percentage will be charged on these contracts," said Charles Sennott, the executive editor of the GlobalPost. "This is so open."
The State Department has spent more than $4 billion on development contracts in Afghanistan since 2002. Experts say the kickbacks could have netted the Taliban tens of millions of dollars and are such an open secret on the streets that the U.S. government had to know.
"You cannot do anything about it," said CBS News consultant Jere Van Dyke. "This is how it operated, this is how it was in the 1980s, this is how it is today."
Contractors have good reason to fear the Taliban. As of last September, 291 State Department-funded contractors, most of them foreigners, had been killed by Afghan insurgents.
The State Department has launched an investigation into the alleged protection payments.
"In Afghanistan, any diversion of funds for any reason makes it that much more difficult for us to achieve our objectives," said P.J. Crowley, an assistant secretary of state for public affairs.
Especially because popular support for the war, which has fallen lately, could sink ever further if taxpayers fear their money is going to fund our adversaries.