LIZ SIDOTI,AP Political Editor

WASHINGTON (AP) - We were one. Or so it seemed - for a while, at least.

"America is united," President George W. Bush proclaimed a decade ago after the horror that terrorists wrought. And it felt that way.

Not Republicans. Not Democrats. Just Americans clinging to one another as we coped with the attacks on our freedom, on our security, on our way of life. We mourned together, raged together, resolved together.

But it wasn't long before the perception of a united America gave way to the reality of division. Political polarization became the norm. And partisanship, gridlock and a loss of faith in institutions returned in force.

As diverse as it is, is this country capable of being truly united? And if we were, would that really be a good thing?

Americans come together spontaneously or, perhaps, instinctively at times of tragedy and trauma. We always seem to be on the same page when it comes to our core principles. We want America to be free. We want America to be secure. And when those tenets are violated, watch out.

Consider the aftermath of the bombing of Pearl Harbor and WWII, perhaps the last time the nation was - or, rather, felt - truly unified. That is, until 60 years later when war came to America again. In the days after Sept. 11, 2001, there was almost unanimous support for going after al-Qaida, an anomaly for an American public that usually agrees on little.

We wanted to win, to make the bad guys lose. At the end of the day, al-Qaida was not targeting Republicans or Democrats. It was killing Americans. And Americans on the whole wanted to fight back.

But was that unity? Or was that simply a hunger, a yearning for it in a nation whose motto for nearly two centuries was the Latin "e pluribus unum" - "Out of many, one"?

Whatever the answer, it was rare - and fleeting. Ten years later, our politics are a lot like they were before 9/11. And, perhaps, worse. Americans, and the leaders we elect, struggle to find common ground, if they're trying at all. At a time when so many hunger for it, is unity anything more than a passing thought?

We face enormous, decades-old problems. Our willing work force can't find jobs. Our housing market is weighing down a fragile economy. We face mounting debt threatening to crush generations ahead. Our safety net - Social Security, Medicare and Medicaid- is in critical condition. Our schools drastically lag behind those of other nations.

Conventional wisdom would say it's frustrating, maybe even sad, that our leaders can't seem to come together to fix these woes - no matter which political party is in power. But it's also totally understandable. A diverse nation of people with vastly different ideas can never truly be unified. And here's something else: Maybe, just maybe, it shouldn't be.

Doesn't a healthy democracy depend on dissenting viewpoints? And don't controlled disagreements make us who we are? Wouldn't actual unity prevent growth in a nation whose best times have come with - or come from - great change?

Yet if unity is unattainable, disunity can be toxic. Just look at this summer's debt debate. It further soured an already surly American public on the ability of the federal government to work, much less solve the nation's problems.

Nevertheless, there are moments when we've spoken together as much as is possible. The period immediately after Sept. 11, 2001, was one of them.

"This will require our country to unite in steadfast determination and resolve," Bush said. It was a call to arms by a president who famously had called himself a "uniter, not a divider."

The following weeks saw Congress pass bipartisan measures to create a Department of Homeland Security and give law enforcement agencies sweeping search and surveillance powers over U.S. citizens. And Americans across the ideological spectrum supported their leaders.

But not indefinitely. That one-nation feeling started unraveling within months as the sense of unity gave way to our differences. Political polarization rose, not just on Capitol Hill but in communities across America. So did anger, particularly over the Bush White House's reasoning for pre-emptively attacking Iraq.

And although many expected it, we didn't get hit again. But we also didn't catch Osama bin Laden or crush al-Qaida quickly. So, predictably, Republicans and Democrats starting seizing on that reality to try to gain power.

"I have no ambition whatsoever to use this as a political issue," Bush said in January 2002.

That same month, White House political adviser Karl Rove urged Republicans to make the war on terrorism central to the fall congressional elections, saying: "We can go to the country on this issue."

Using that playbook, Republicans took control of Congress. In one remarkable race in Georgia, Republican Saxby Chambliss won a Senate seat after painting Democratic Sen. Max Cleland, who lost both his legs and an arm in Vietnam, as weak on national security in part by airing a much-maligned TV ad that included images of Saddam Hussein and bin Laden.

After the 2002 election, a Pew Research Center survey showed that partisan polarization had reached a new high as both Republicans and Democrats became more intense in their political beliefs. That helps explain why the 2004 presidential race so split the country. The campaign was centered on 9/11, national security and questions of character.

It was an aggressive campaign and a close election, underscoring how far from united the states of America had become.

The partisan polarization persisted well into Bush's second term. By January 2006, Rove was vowing to again make the "war on terror" a central campaign issue, saying: "Republicans have a post-9/11 view of the world. And Democrats have a pre-9/11 view of the world."

It didn't work. Democrats swept back into power, taking control of both the House and Senate. The country was divided, and bitterly so.

Then came Barack Obama. He stoked the notion of unity from Day One of his presidential campaign with these words: "In the face of a politics that's shut you out, that's told you to settle, that's divided us for too long, you believe we can be one people, reaching for what's possible, building that more perfect union."

Obama, a Democratic senator from Illinois, invoked the 9/11 attacks, spoke to our common principles and, perhaps, seized upon our yearning for unity, saying: "Politics doesn't have to divide us on this anymore - we can work together to keep our country safe."

People flocked to him. His message resonated. And he won the presidency.

As Obama took office, the Pew Research Center found that public expectations for partisan cooperation were as great as they were in January 2002. But that feeling didn't last, either. As Americans mark a decade since Sept. 11, 2001, who among us thinks that the nation today is one of unity, of a single sense of purpose?

In May, as he announced that American forces had killed bin Laden, Obama re-summoned that spirit. "Tonight," he said, "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."

And, for a few hours, most of the United States of America again felt united - even if we never really were, even if that's a notion that a seething, bubbling, contentious democracy of 300 million people can never really achieve.

EDITOR'S NOTE - Liz Sidoti, the political editor for The Associated Press, has covered national politics for the AP since 2003. Tomorrow: New Yorkers and 9/11, and how they process it 10 years later.