Democrats jeered when John McCain told a New Hampshire audience during the 2008 presidential campaign that he would be glad to see US troops remain in Iraq for decades, even a century, once the war was over. “We’ve been in Japan for 60 years [and] in South Korea for 50 years,” he said. A similar long-term stay in a postwar Iraq, buttressing allies and providing stability in a volatile region, would “be fine with me as long as Americans are not being injured or harmed or wounded or killed.”

McCain’s political foes had a field day with that. Though he had plainly been speaking of a friendly peacetime presence, Democrats hammered him as an insatiable warmonger. Then-Senator Barack Obama claimed the Arizona Republican was “willing to send our troops into another 100 years of war in Iraq.” Howard Dean, the Democratic Party chairman, declared: “McCain’s strategy is a war without end.” In a TV ad aired by MoveOn.org, a new mother, playing with her baby boy, told McCain that if he was counting on using her little Alex as cannon fodder in Iraq, “you can’t have him.”

Yet McCain was right. Having won a difficult war in Iraq, the United States should have settled in for the long haul, just as we did in Japan, Germany, Italy, and South Korea, where tens of thousands of American troops remain to this day. Instead President Obama pulled the troops out, as he had always made clear he would. Iraq’s fragile constitutional democracy, so hard-won, was left to fend for itself. Al Qaeda in Iraq, all but wiped out, gained a new lease on life. Now a new generation of Americans, including young Alex, is learning that the loss of US influence makes the world a more menacing place.

We are nearly five years into a presidency whose foreign policy is driven by the conviction that America’s profile in the world, above all the Muslim world, must be lowered. “One of the things I intend to do as president is restore America’s standing in the world,” Obama vowed as he pursued the presidency in 2008. Abandoning Iraq wasn’t the way to do it. America’s standing in the world has reached a new low. So low that even Bashar al-Assad can thumb his nose at an explicit presidential “red line” – then laugh as Vladimir Putin effortlessly suckers Washington into doing nothing about it.

George W. Bush made plenty of mistakes, but he understood the difference between leading and “leading from behind.” When he went to Congress for authorization to remove Saddam Hussein from power, he got it. When he told Saddam to leave Iraq or be forcibly overthrown, he made good his threat. When he explained the need for military action, he didn’t need to reassure Americans that their commander-in-chief “doesn’t do pinpricks.”

All American presidents engender resentment and opposition on the world stage. It goes with the job of leading the world’s superpower. Yet Obama was certain that the world couldn’t help but adore an America wise enough to elevate him to the White House. From his earliest days as a presidential candidate, Obama had argued that Bush had eroded America’s international status by waging a “dumb” war in Iraq and showing insufficient respect for diplomatic engagement. He would reverse course, he promised voters, and that would make everything better. “The world will have confidence that I am listening to them, and that our future and our security is tied up with our ability to work with other countries.”

But what the world has learned from listening to Obama is that he confuses moral preening with effective leadership. That he is deeply uncomfortable with America’s military preeminence. That it’s not hard to call the bluff of this president who says he doesn’t bluff.

And that he still doesn’t realize how much harm was set in motion by the wholesale withdrawal from Iraq. As the US military walked away, internal Iraqi politics grew more authoritarian. Sunni terrorism revived. Al-Qaeda in Iraq started sending offshoots into Syria. Iraqi Shiites, meanwhile, lost their American buffer against Iran. “If American airpower were still in Baghdad,” writes Reuel Marc Gerecht of the Foundation for Defense of Democracies, “Tehran could not resupply Syria and Lebanese Hezbollah by air, and the Assad regime would lose the two resources most critical to its survival.”

A long-term US presence could have been such a blessing for postwar Iraq, nurturing Arab democracy and moderation, giving peace and prosperity the chance they were given in Germany, Japan, and Korea. Instead we walked away, undercutting our friends and our reputation, and leaving a vacuum the region’s worst brutes moved to fill.

(Jeff Jacoby is a columnist for The Boston Globe).