By Liz Sidoti, AP national political writer

WASHINGTON — At last, something big to celebrate and lift America’s mood.

A nation surly over rising gas prices, stubbornly high unemployment and nasty partisan politics poured into the streets to wildly cheer President Barack Obama’s announcement that Osama bin Laden, the world’s most wanted man, had been killed by U.S. forces after a decade-long manhunt.

The outcome could not have come at a better time for Obama, sagging in the polls as he embarks on his re-election campaign. For now, at least, he is assured of a big political boost, something that could strengthen his hand as he heads into a big battle over federal spending with Republicans who control the House.

Outside the White House, hundreds of people chanted “U-S-A! U-S-A!” and waved American flags. And in New York City at ground zero, where al-Qaida downed the twin towers, a crowd broke out into song, including renditions of “The Star-Spangled Banner” and “I’m Proud to be an American.”

The joyous response won’t last forever but on this day, the nation’s spirits were lifted and a country sharply divided along partisan lines seemed united much as it was in the aftermath of the Sept. 11, 2001, attacks that bin Laden orchestrated.

That was not lost on Obama.

“Let us think back to the sense of unity that prevailed on 9/11. I know that it has, at times, frayed. Yet today’s achievement is a testament to the greatness of our country and the determination of the American people,” Obama said Sunday in a late night statement urging the nation to come together again.

Former President George W. Bush had promised to get bin Laden dead or alive but wasn’t able to achieve his goal. Obama picked up the challenge and, as a candidate for president, vowed that “We will kill bin Laden.”

Obama’s persistence — and success — makes it more difficult for political foes to question whether he is tough enough to do whatever it takes to keep America safe, and whether he’s experienced enough to be commander in chief.

For Republicans seeking the presidency, it will more difficult to question his strength on national security and foreign policy.

Perhaps reflecting Obama’s enhanced standing if not newfound respect, even Republicans praised him.

Said Rep. Eric Cantor, the No. 2 Republican in the House: “I commend President Obama who has followed the vigilance of President Bush in bringing bin Laden to justice.” And former Minnesota Gov. Tim Pawlenty, an all-but-declared presidential candidate, congratulated Obama for “a job well done.”

Beyond America, bin Laden’s death sends a clear signal to the rest of the world about the persistence of U.S. power and that no one is beyond the United States’ reach.

To that end, Obama put the world on notice, saying: “We will never tolerate our security being threatened, nor stand idly by when our people have been killed. We will be relentless in defense of our citizens and our friends and allies.”

But while bin Laden’s death closes one chapter in the U.S. war against terrorism, it also opens others and raises a slew of questions.

• Will the relationship between Pakistan and the United States be strong or weak once the dust settles? The United States did not give Pakistan advance notice that American forces would stage the raid.

Bin Laden was found living in a huge fortified compound in an affluent Pakistani town about 60 miles from Islamabad. The compound was located about 100 yards from the gates of a Pakistani military academy — certain to raise questions about al-Qaida’s ability to build a custom-made hideout in such proximity.

• Will bin Laden’s killing make the United States more likely to pull its troops out of Afghanistan?

Said Obama: “There’s no doubt that al-Qaida will continue to pursue attacks against us. We must — and we will — remain vigilant at home and abroad.”

And, for now, at least united.