Democratic hawks believe that America has a crusading mission to champion humanitarian intervention. Their credo is exemplified by former Secretary of State Madeleine Albright’s reference to America as the “indispensable nation,” one that should intervene abroad whenever and wherever necessary to defend the oppressed. Count among the hawks New York Times commentator Bill Keller, who has been demanding intervention in Syria; Anne-Marie Slaughter, former director of policy planning at the State Department; and Sen. Carl Levin (D-Mich.), a staunch liberal who heads the Senate Armed Services Committee and is urging limited military strikes on Syria.

On the other side are the realist skeptics of intervention in Syria, such as Defense Secretary Chuck Hagel. And although Secretary of State John F. Kerry wants to bolster the Syrian rebels, he’s not big on regime change; he favors increased aid as a measure to strengthen diplomatic efforts to force President Bashar Assad to negotiate.

Both men have been deeply shaped by the Vietnam War, in which they served with distinction, and the Iraq war. The fear of a repetition of Iraq is what is prompting liberal pundits such as David Rieff to plead, “Save us from the liberal hawks.” The liberal realists worry that the very military steps taken to help embattled populations abroad may inadvertently end up triggering even greater havoc. Like John Quincy Adams, they believe “America does not go abroad in search of monsters to destroy” for fear that America itself will become the monster.

The conflict between the two camps is probably best understood as the latest installment in a running dispute over the lessons of the Vietnam War. Vietnam was originally promoted by Cold War liberals such as Dean Acheson and Dean Rusk. A younger generation, led by Sen. George McGovern (D-S.D.), said that the U.S. had lost its way in Southeast Asia and was becoming an international bad guy. The warriors recoiled. Some became neoconservatives and left for the GOP; others remained behind to try to stage an insurgency inside the party.

Ever since, the Democratic Party has been divided when it comes to foreign policy. During the 1970s and ’80s, the doves mostly had the upper hand, decrying U.S. militarism everywhere, from the invasion of Grenada to the Nicaraguan revolution. It may have been emotionally satisfying, but the Democrats also looked weak on foreign policy, a vulnerability that Ronald Reagan, George H.W. Bush and George W. Bush exploited.

Then came the Clinton administration. Initially, Secretary of State Warren Christopher and National Security Advisor Anthony Lake, both of whom were scarred by Vietnam, kept America out of the conflict. But as atrocities mounted in the Balkans, the calls for intervention, including from Samantha Power, who made her name as a journalist covering Serbian aggression, and from Albright, then ambassador to the U.N., became increasingly prominent. In 1995, the administration intervened militarily in the Balkans to bring the Serbs to heel. Hand-wringing about American power was out. A new taste for intervening abroad under the banner of humanitarianism was in. The liberal hawks were once again ascendant.