President Obama’s declaration late Sunday night that U.S. forces in Pakistan had killed Osama bin Laden will likely prove one of the most significant moments in his presidency.

Speaking from the White House’s East Room shortly before midnight EST, the president offered the nation a long-desired moment of closure nearly a decade after the horrors of the 9/11 attacks.

“Tonight, let us think back to the sense of unity that prevailed on 9/11. I know that it has, at times, frayed,” Obama declared in announcing bin Laden’s death. “Yet today’s achievement is a testament to the greatness of our country and the determination of the American people… We are once again reminded that America can do whatever we set our mind to.”

Obama was careful not to gloat about the breakthrough for the struggle against Islamist terrorism–indeed, he went so far as to praise to his predecessor, former President George W. Bush, who Obama had frequently assailed for bungling that struggle on the 2008 campaign trail. At the same time, though, as the smoke begins to clear from this pivotal moment, a no-less significant question lingers: How will the al Qaeda leader’s death alter the nation’s political landscape, especially ahead of next year’s 2012 presidential campaign?

The short answer, of course, is that it’s far too early to say for sure. To be sure, as news cameras capture footage of cheering crowds across party lines gathering to celebrate bin Laden’s demise, Obama seems almost certain to experience a bump in national approval for his handling of the situation. And the country’s mood–usually measured in so-called “right track/wrong track” numbers–will likewise trend upward with a major shot of good news after weeks of angst over issues such as rising gas prices and the struggling economy.

And as the president gears up for his 2012 re-election bid, he can take assurance in his ability to brandish a significant foreign policy achievement: He personally signed off on a mission to capture the world’s most wanted terrorist, and it was successful. Obama will be certain to remind voters about that milestone at every opportunity–knowing that it’s bound to loom larger in the public mind than the last several months’ worth of hand-wringing among candidates and pundits over this administration’s approach to Libya and the tumultuous war in Afghanistan.

Many of Obama’s likely GOP rivals in 2012 have lambasted him in recent weeks as a president with a weak foreign-policy dossier. But last night, some of his potential opponents–including Tim Pawlenty and Mitt Romney–carefully offered Obama praise for his handling of the bin Laden operation.

“In the hours after the 9/11 attacks, President Bush promised that America would bring Osama bin Laden to justice–and we did,” Pawlenty said in a statement. “I want to congratulate America’s armed forces and President Obama for a job well done. Let history show that the perseverance of the US military and the American people never wavered.”

In a message posted on Facebook, Romney called bin Laden’s death a “great victory great victory for lovers of freedom and justice everywhere.” “Congratulations to our intelligence community, our military and the president,” he wrote.

But not all GOP candidates were as gracious. In separate messages on Twitter and Facebook, Sarah Palin made no mention of Obama, instead praising the military. “Thank you, American men and women in uniform. You are America’s finest and we are all so proud,” she wrote. “Thank you for fighting against terrorism.”

However, political history also offers some important cautions about how short-lived such victories can be in the heat of a re-election effort. Take, for example, former President George H.W. Bush’s sky-high poll numbers in the aftermath of the successful 1991 Gulf War, which made him seem virtually unbeatable against his likely Democratic opponents.

But as the 1992 campaign drew closer, Bush 41’s numbers steadily dropped, and lost his bid for a second term, thanks mostly to public anxiety over the struggling economy–an issue that also seems likely to dominate the upcoming 2012 campaign, at least for now.

In policy terms, too, the administration seem averse to gloating over the legacy of his historic moment. Last night, Obama made clear in his remarks that the war in terror is far from over–and that bin Laden’s death doesn’t mean an end to threats to the nation. “His death does not mark the end of our effort,” the president warned. “There’s no doubt that Al Qaeda will continue to pursue attacks against us. . . . The cause of securing our country is not complete.”

(Photo of Obama: Brendan Smialowski-Pool/Getty Images)