Afghanistan is not Vietnam.

True enough.

But does that obvious truth mean that there are no lessons from our experience in Vietnam? Are there no haunting legacies that affect today’s leaders?

Does the Vietnam War have an impact on Americans as they decide on actions in Iraq, Afghanistan, Syria, Iran, and other places that call for the application of our military might?

In their recent book, “Haunting Legacy: Vietnam and the American Presidency from Ford to Obama,” former prominent journalist Marvin Kalb and his daughter, Deborah, explain how Vietnam has been an important factor in the decision-making of every president since John Kennedy.

Lyndon Johnson and Richard Nixon had to deal directly with the reality of that war, which each ultimately determined could not be won.

Gerald Ford had to watch while Saigon fell. He felt compelled to demonstrate that the U.S. still had the might and the will to crush any country that challenged our interests. In response to the seizure of a U.S. merchant ship by Cambodian pirates, he launched overwhelming force in a risky but successful operation.

On the other hand, Jimmy Carter, responding to the loss in Vietnam, aimed to keep the United States out of military conflict. However, unprecedented events in Iran forced him to change his posture and attempt a rescue of the embassy hostages. The failure of that mission tarnished Carter’s presidency and left open the question of whether the U.S. had the resolve to respond militarily to challenges to our interests.

Ronald Reagan was more cautious than his forceful rhetoric when he decided not to respond and punish those who killed 241 Marines in Lebanon. Worried about the possibility of other Vietnams, he pushed for development of what became the Powell Doctrine. It set out guidelines that limited the use of force to vital national interests, only as a last resort, with clear objectives, and overwhelming force that would assure success.

George H. W. Bush adopted the Powell Doctrine and applied it successfully to guide the country’s response to Iraq’s seizure of Kuwait. He then resisted pressure to continue the military operation once the “clear” objectives had been obtained.

Burned by an early humiliating loss of troops on a humanitarian mission in Somalia and conditioned as a young opponent of the Vietnam War, Bill Clinton decided that he would not put combat troops on the ground, where they could get bogged down without an exit plan. Rather he sought to achieve objectives by air attacks.

On the other hand, George W. Bush, confronting challenges in Afghanistan and Iraq, seemed eager to show that the memories of Vietnam would not keep the U.S. from using ground forces to subdue its adversaries. He accepted or did not consider the unintended consequences of two long-term counterinsurgency operations.

Barack Obama inherited these two counterinsurgency or nation-building efforts. He learned from experience what Vietnam had already taught. If those types of operations can ever be successful, they require a long-term, solid commitment without a fixed deadline.  Another lesson he might have learned from Vietnam: Americans want to win, but they will not accept a permanent war with an ongoing loss of American lives.

The Kalbs quote one president whose writings in 1999 might be good guidelines for his successors. “Our nation should be slow to engage troops. But when we do so, we must do so with ferocity. We must not go into a conflict unless we go in committed to win. We can never again ask the military to fight a political war. If America’s strategic interests are at stake, if diplomacy fails, if no other option will accomplish the objective, the Commander in Chief must define the mission and allow the military to achieve it.”

If only George W. Bush had followed the wisdom in his own words.