It was just as deeply etched in the minds of commentators and citizens. Just days before the U.S.-led coalition invaded Iraq in 2003, one liberal e-mailed to me, “This is just like Vietnam.” It wasn’t, of course, and it isn’t. But that was his only frame of reference, and we instinctively look to the country’s last war to provide guidance on how to fight the next one.

Today, General Petraeus is a big reason Vietnam is receding, because he authored the biggest, most important change in recent years.

At the end of 2006, the war in Iraq looked as if it could end in disaster for our country. The Iraq Study Group recommended the U.S. “begin to move its combat forces out of Iraq responsibly,” code for “accept defeat.”

Petraeus outlined a new approach, the “surge,” which involved securing areas and holding them. Many senators, including Obama and his vice presidential pick, Joe Biden, opposed it. “The president and others who support the surge have it exactly backwards,” Biden said in December 2006. He urged dividing Iraq into three partially autonomous ethnic regions.

As recently as this spring, Biden added, “There is little evidence the Iraqis will settle their differences peacefully any time soon.” And maybe that’s true. But they have a chance to, and the U.S. can emerge victorious. Because of Petraeus and his leadership in Iraq, there’s a new benchmark to measure future military engagements against. Vietnam is less important than ever.

“During a crisis, more than at any other time,” Petraeus wrote in 1987, “a nation is its decision makers; and they, due to the stress and incomplete information associated with crises, are very likely to seek guidance or insights from the past.”

Americans should remember that, as we select our next decision maker.