IT WASN'T so long ago that erstwhile supporters of the war in Iraq were invoking hindsight to justify their newfound opposition to it. "Obviously if we knew then what we know now," Senator Hillary Clinton said in December 2006, when asked whether she regretted her 2002 vote authorizing military action, "I certainly wouldn't have voted that way."
Many of Clinton's colleagues said the same thing. An ABC News survey of senators in January 2007 found that "an overwhelming number" of Democrats who had voted in favor of going to war - including Joe Biden of Delaware, Chris Dodd of Connecticut, John Breaux of Louisiana, and Jay Rockefeller of West Virginia - had had a change of heart.
Liberals and Democrats weren't the only ones going wobbly. "If I had known then what I know now about the weapons of mass destruction," Texas Senator Kay Bailey Hutchison, a Republican, told the Houston Chronicle, "I would not vote to go into Iraq." The conservative columnist Jonah Goldberg pronounced the Iraq war "a mistake by the most obvious criteria: If we had known then what we know now, we would never have gone to war with Iraq." Others singing from the same hymnal have included Jonathan Rauch, National Journal's respected semi-libertarian essayist, and (somewhat earlier) Michael Howard, the former leader of the British Conservative Party.
The prevailing wisdom 18 months or so ago was that invading Iraq had been, in retrospect, a disastrous blunder. It had led to appalling sectarian fratricide and an ever-climbing body count. Iraqi democracy was deemed a naive pipe dream. Worst of all, it was said, the fighting in Iraq wasn't advancing the global struggle against Islamist terrorism; by rallying a new generation of jihadists, it was actually impeding it. Opponents of the war clamored loudly for pulling the plug - even if that meant, as The New York Times acknowledged in a bring-the-troops-home-now editorial last July, "that Iraq, and the region around it, could be even bloodier and more chaotic after Americans leave."
But what if we had known then what we know now?
We know now that the overhauled counterinsurgency strategy devised by General David Petraeus - the "surge" - would prove spectacularly successful, driving Al Qaeda in Iraq from its strongholds, and killing thousands of its fighters, supporters, and leaders.
We know now that US losses in Iraq would plummet to the lowest levels of the war, with just five Americans killed in combat in July 2008, compared with 66 fatalities in the same month a year ago - and with 137 in November 2004.
We know now that the sectarian bloodletting would be dramatically reduced, with numerous Sunni tribal leaders abandoning their former Al Qaeda allies, and Shi'ite radical Moqtada al-Sadr's Mahdi Army being thoroughly routed by the Iraqi military.
We know now that by the summer of 2008, the Iraqi government would meet all but three of the 18 benchmarks set by Congress to demonstrate security, economic progress, and political reconciliation.
And we know now that, far from being undermined by the campaign in Iraq, the wider war against Islamist violence would show significant progress, with terrorism outside Iraq's borders having "in fact gone way down over the past five years," as Newsweek's Fareed Zakaria noted in May - and with popular support for jihadist organizations plummeting across the Muslim world.
So what does hindsight counsel today? That Iraq is a pointless quagmire - or that it is a costly but winnable war, in which patience, tenacity, and smarts have a good chance of succeeding?
Hindsight isn't always 20-20, particularly in wartime, when early expectations of an easy rout can give way to an unexpectedly long and bloody grind - and when victory has so often been achieved only after persevering through strategic debacles, intelligence failures, and wrenching battlefield losses.
There are no guarantees in Iraq. As with every war, we will know for sure how it ends only after it ends. But an effort that so many critics sourly have called the worst foreign-policy blunder in American history - the drive to emancipate Iraq from a monstrous and dangerous dictatorship and transform it into a reasonably civilized, law-abiding democracy - looks increasingly like a mission nearly accomplished. Had we known six years ago what we know today, would we have done it? Differently, no doubt. But we would have done it.
Jeff Jacoby can be reached at firstname.lastname@example.org.