The New York Times reports today on a still-classified CIA report, commissioned by the Obama administration during the debate in 2012 and 2013 over whether to increase U.S. support for the anti-Assad rebels in Syria. Senior officials tell the Times that the report “concluded that many past attempts by the agency to arm foreign forces covertly had a minimal impact on the long-term outcome of a conflict. They were even less effective, the report found, when the militias fought without any direct American support on the ground.”

Obama referred to this report in an interview with the New Yorker’s David Remnick last year, saying, “Very early in this process, I actually asked the CIA to analyze examples of America financing and supplying arms to an insurgency in a country that actually worked out well. And they couldn’t come up with much.”

The best example they found was the support for the anti-Soviet mujahideen in Afghanistan in the 1980s, which eventually forced a Soviet withdrawal from the country. But Afghanistan’s subsequent experience doesn’t exactly make that an encouraging case study.

The fact that the president and his advisers are talking about the unreleased document may be part of a plan to counter a line of criticism voiced by, among others, former Secretary of State Hillary Clinton and former Secretary of Defense Leon Panetta. That criticism—that the situation in Syria wouldn’t have spiraled out of control if the U.S. had provided more aid to the “moderate” rebels sooner—is contradicted by the CIA’s report.

The CIA’s assessment jibes with the academic literature on the topic, as George Washington University political scientist Marc Lynch recently wrote on the Washington Post’s Monkey Cage blog:

In general, external support for rebels almost always make wars longer, bloodier, and harder to resolve. … Worse, as the University of Maryland’s David Cunningham has shown, Syria had most of the characteristics of the type of civil war in which external support for rebels is least effective. The University of Colorado’s Aysegul Aydin and Binghamton University’s Patrick Regan have suggested that external support for a rebel group could help when all the external powers backing a rebel group are on the same page and effectively cooperate in directing resources to a common end. Unfortunately, Syria was never that type of civil war.

The U.S. occasionally aided anti-communist rebel groups throughout the Cold War—the Bay of Pigs invasion was a notable example—but it really ramped up its support with the “Reagan doctrine” of the 1980s, which involved countering Soviet support for leftist governments in the developing world by funding anti-Communist rebel groups. In addition to Afghanistan, the CIA funneled arms and money to anti-Communist rebels in Nicaragua and Afghanistan.

In the context of the Cold War, there’s an argument to be made that this strategy worked—the Soviet Union collapsed, after all—but in the actual conflicts, the outcomes were ambiguous and the wars longer and bloodier than they might have been otherwise. (Angola’s civil war lasted 27 years.)

The study of history might have led to the White House’s reluctance to have the CIA provide direct aid to the rebels. The agency, though, was involved in facilitating aid from others, Arab governments and Turkey in particular, who may have been less discriminating about the recipients of that support than the U.S. might have been. When future historians ponder the lessons of this engagement, they may conclude that historical examples led the U.S. away from one set of mistakes and toward a whole different set of errors.