Polls go up and down. President Obama’s “bounce” from the killing of Osama bin Laden is already starting to recede. But the last two weeks have redefined Obama’s presidency and enhanced his re-election prospects.

The images generated by the president — his dramatic late-night announcement from the White House, his wreath-laying at Ground Zero, his rousing speech before 2,000 cheering soldiers at Fort Campbell, his interview on “60 Minutes” — will all endure long after his ratings return to normal.

Those images are already part of our national history and mythology. They are permanently collected and instantly available (for free) on YouTube. And it’s a sure bet that they will appear countless times in paid commercials and Web videos promoting Obama next year.

Indelible images are a critical part of any presidency, for good or ill. When George W. Bush grabbed that bullhorn just days after 9/11, he sent a message of courage and resolve that rallied the American people. But when he flew over the devastation caused by Hurricane Katrina, he conveyed an attitude of remoteness and neglect that torpedoed his presidency beneath the waterline.

In 1979, when 66 American hostages were seized in Tehran — and paraded blindfolded through the streets — the symbolic display of American weakness fatally damaged Jimmy Carter’s re-election prospects. Eight years later, when Ronald Reagan stood at Berlin’s Brandenburg Gate and demanded, “Mr. Gorbachev, tear down this wall,” he embodied a renewed sense of American strength and determination.

Obama has lacked a defining moment, an episode and an image that says, “I am president, I am commander in chief, I am capable of filling the frame and handling the job.” Now he has one. He is Obama of Abbottabad.

Democratic pollster Peter Hart told NBC News that bin Laden’s demise could become “a possible … tipping point” for Obama’s presidency. David Axelrod, the president’s closest political adviser, emphasized the moment’s symbolic value to the New York Times: “It was a reaffirmation of that American determination and American spirit — the ability to do the things that some people thought impossible. And that has value.”

Yes, it does. Democrats have long struggled with the label “weak on defense,” and for good reason. Lyndon Johnson’s disastrous use of American power in Vietnam left a generation of party leaders timid and traumatized. Carter failed miserably in rescuing the hostages in Iran. Bill Clinton couldn’t even salute right and dithered indecisively before finally committing to battle in the Balkans.

By vowing to capture bin Laden “dead or alive,” and then failing to make good on his threat, Bush gave Obama an opportunity to exorcise those Democratic demons. And in his revealing interview with “60 Minutes,” the president described his determination to seize that chance.

“Shortly after I got into office,” he said, “I brought (CIA chief) Leon Panetta into the Oval Office and I said to him, ‘We need to redouble our efforts in hunting bin Laden down. And I want us to start putting more resources, more focus and more urgency into that mission.’”

Once bin Laden was dead, Team Obama put a lot of resources and urgency into solidifying the political benefits of that success. Republicans have always known the value of surrounding themselves with people in uniform, and now Obama has his own set of images that identify him with symbols of honor and heroism, from firefighters in Manhattan to paratroopers in Kentucky.

In case anyone missed all the visual cues, Obama on “60 Minutes” referred repeatedly to the assault team as “our guys.” Only a few questions remain: Who plays Obama in the movie version of “SEAL Team Six”? Does it come out before November 2012? And is Obama a sure shot for re-election?

The answer to the last one is no. Not with 9 percent unemployment and $4 gasoline. In the latest NBC poll, only one out of three Americans says the country is headed in the right direction, and fewer than four in 10 approve of Obama’s handling of the economy. Pollster Hart says those numbers should “frighten the president as he looks ahead to re-election.” And he’s right. They should.

Moreover, Pakistan is far removed from the daily lives of ordinary Americans. Most of them could not even find it on a map. When they vote, jobs will weigh more heavily than jihadists. But a basic fact of political life has changed. Obama of Abbottabad has acted decisively and won a victory. His challengers have yet to prove themselves. He is president, and they are still pretenders.

(Steve and Cokie’s new book, “Our Haggadah” (HarperCollins), was published this spring. Steve and Cokie Roberts can be contacted by email at stevecokie@gmail.com.)