“Do we really need to be spending $120 billion in a country with a G.D.P. that’s one-sixth that size?” asked Brian Katulis, a national security expert at the Center for American Progress, a policy group with close ties to the Obama administration. “Most Americans would be shocked to know that we’re spending that kind of money for jobs programs for former Taliban, and would wonder where are our jobs programs for Detroit and Cleveland?”

In 2010, Congress — at the Obama administration’s request — set aside $100 million to support programs in Afghanistan aimed at moving former insurgents off the battlefields and into the country’s mainstream economy. Those efforts — similar to what the Bush administration did in Iraq — have yet to bear much fruit; the 1,700 fighters who have enrolled in the reintegration program represent only a fraction of the estimated 20,000 to 40,000 Taliban insurgents, The New York Times reported Monday.

Most American aid bypasses the Afghan government and goes to international companies, a practice that, according to a June 8 report by the Senate Foreign Relations Committee, can undercut the Afghan government and lead to redundant and unsustainable donor projects. But Obama administration officials complain that the Afghan government of President Hamid Karzai has, thus far, been unwilling to tackle corruption in any meaningful way, making it hard to argue that it should get more money directly.

In Washington, the argument over whether the United States should be building bridges in Kandahar or Cleveland is bound to grow even louder as the 2012 election campaign heats up.

After Senator Manchin made his speech on Tuesday calling for an end to nation-building in Afghanistan, Senator John McCain, Republican of Arizona, took to the floor to rebuke him, calling Mr. Manchin’s remarks characteristic of the “isolationist-withdrawal-lack-of-knowledge-of-history attitude that seems to be on the rise.”

But in Mr. McCain’s own Republican Party, which has historically been more supportive of both the Iraq and Afghanistan wars than Democrats, there is clearly some queasiness about war spending during a period of economic distress.

Four years ago, Representative Ron Paul of Texas was the only Republican presidential candidate raising concerns about the costs of the Afghanistan or Iraq wars. But last week, Mr. Paul was joined explicitly by another contender, Jon M. Huntsman Jr., the former governor of Utah and the Obama administration’s former ambassador to China, who said that the cost of a continued military presence was a leading factor in his belief that a major troop drawdown should begin in Afghanistan.