WASHINGTON — On Monday, the bipartisan leaders of Congress are scheduled to gather with colleagues at noon for a ceremony marking the terrorist attacks of Sept. 11, 2001. It will be reminiscent of the gathering on the night of the attacks, when members of Congress, many holding small American flags, stood on the Capitol steps and spontaneously sang "God Bless America." But so much has changed.

Twenty years ago, members of Congress were joined in a determined and resilient expression of national unity at an unprecedented moment in the nation's history, a day that brought deaths and heroism but also shock, fear and confusion. Monday's ceremony will no doubt be somber in its remembrance of what was lost that day, but it will come not as expression of a united America but simply as a momentary cessation in political wars that rage and have deepened in the years since those attacks.

In a video message to Americans released Friday, President Joe Biden spoke of how 9/11 had united the country and said it was represented "America at its best." He called such unity "our greatest strength," while noting it is "all too rare." The unity that followed the attacks didn't last long. Americans reverted more quickly than some analysts expected to older patterns of partisanship. With time, new divisions over new issues have emerged, which now make the prospect of a united nation ever more distant.

The question is often asked, as America has plunged deeper into division and discord, is there anything that could spark a change, anything big enough to become a catalyst for greater national unity? But if 9/11 doesn't fit that model, then what does? And look what happened in the aftermath of that trauma.

For a time, the shock effect of the attacks did bring the country together. Then-President George W. Bush's approval ratings spiked to 90% in a rally-round-the-flag reaction that was typical when the country is faced with external threats or crises.

One notable expression of the unity at the time came from Al Gore, the former vice president who had lost the bitter 2000 election to Bush after a disputed recount in Florida and a controversial Supreme Court decision.

Speaking at a Democratic Party dinner in Iowa less than a month after the attacks, Gore called Bush "my commander in chief," adding, "We are united behind our president, George W. Bush, behind the effort to seek justice, not revenge, to make sure this will never, ever happen again. And to make sure we have the strongest unity in America that we have ever had." The Democratic audience rose, applauding and cheering.

Trust in government rose in those days after the attacks. Shortly after 9/11, trust in government jumped to 64%, up from 30% before the attacks, according to Public Opinion Strategies, a Republican polling firm that was closely tracking public attitudes to the attacks, By the summer of 2002, POS found that trust had fallen back, to 39 percent.

Five years after the attacks, then-Sen. John McCain, R-Ariz), now deceased, was quoted as saying that America was "more divided and more partisan than I've ever seen us." Today, after many contentious elections, political warfare over economic, cultural and social issues and an attack on the Capitol last Jan. 6, many Americans would say things have gotten worse.

As he prepared the U.S. response to the attacks by al-Qaida in the fall of 2001, Bush made clear the United States would go it alone if necessary, assembling what was called a "coalition of the willing." He put other nations on notice, saying the United States would be holding them accountable in the campaign against the terrorists. "You're either with us or against us in the fight," he said.

Bush described the world in Manichaean terms, a world of good versus evil. Today's politics at home is often practiced that way. That phrase — "with us or against us" — could stand as a black-and-white expression of the way in which many Americans approach the political battles: All in with the team, red or blue, or not in at all. If you win, I lose. No middle ground.

Lack of imagination had helped to allow 9/11 to happen. No one in the upper reaches of government seemed to have envisioned foreign terrorists hijacking airplanes, turning them into massive jet-fuel-filled weapons and crashing them into buildings, though there had been warnings.

If the response in the years that followed was often chaotic or ill-advised, if things seemed to get worse rather than better, the public demeanor of leaders remained one of total confidence. That was true of one president after another about Afghanistan, as a secret history of the war has since shown. Eventually, as events told a story that contradicted official assurances, the certitude of the leaders gave way to disillusionment and cynicism on the part of citizens. It happened during Vietnam and happened again with Afghanistan and Iraq.

So much went wrong.

In the days after the attacks, politicians noted America's vulnerability — two oceans were no longer protection against foreign attack — and vowed to make perpetrators pay. It was a time of extravagant predictions. Chuck Hagel, then a Republican senator from Nebraska and later defense secretary in the Obama administration, said, "We are forever changed."

More Americans say now that change was for the worse than for the better, according to a recent Washington Post-ABC News poll. Six months after the attacks, two in three Americans said the country had changed for the better.

The mission in Afghanistan morphed from hunting terrorists, subduing the Taliban and bringing Osama bin Laden to justice to one of nation building and a 20-year commitment of U.S. forces that ended last month, amid controversy over Biden's handling of the exit and a public conclusion that the war was not worth fighting. On the night of 9/11, George Tenet, then the CIA director, said to Bush and other senior officials as they contemplated how to respond, it was time to tell the Taliban we're finished with them. Today, the Taliban once again control Afghanistan.

Afghanistan was never enough. The Bush administration quickly shifted its focus to a wider war on terrorism. Even in the days after Afghanistan, Iraq was always in the conversation. In his 2002 State of the Union address, Bush described Iraq, Iran and North Korea and "an axis of evil." He suggested that what he had launched in Afghanistan would expand in scope and lengthen in time. "Our war on terror has well begun," he said, "but it is only begun."

The next year, the United States invaded Iraq. Among those who opposed that invasion was Gore, though he had supported Bush's father's war against Iraq in 1991, unlike Biden, whose positions were the opposite. The invasion was based on what turned out to be a lie, that there was credible intelligence evidence that Iraqi President Saddam Hussein had a stock of weapons of mass destruction. After Saddam was ousted, U.S. officials tried to remake Iraq in a misguided and bungled effort to bring western-style democracy and institutions to that country.

Enemy combatants captured in the war on terror were subjected to torture during harsh interrogation in secret black sites, later exposed, elsewhere in the world. Critics like McCain called those techniques illegal and a stain on America. A Senate committee later concluded that torture had produced no useful intelligence. There was the scandal at Abu Ghraib prison in Iraq, where photos of the mistreatment of Iraqi prisoners by U.S. soldiers drew worldwide condemnation that further soured the public.

Confidence was undermined in other ways. At home, a hasty effort to create the Department of Homeland Security ended up cobbling together a host of organizations that produced a dysfunctional agency whose role and mission remain a point of contention. Only a year ago, Jeh Johnson, who served as DHS secretary in the Obama administration, said that the agency's headquarters bureaucracy "is still a work in progress."

There were successes. During the Obama administration, bin Laden was killed at a compound in Pakistan. Over these many years, there were no major attacks from foreign terrorists against the homeland, no small achievement. Presidents from Bush to Obama to Donald Trump went after terrorist groups and individuals in one country after another with Special Operations forces and drone attacks.

Meanwhile, on the political front, the war on terror, which had first united the country, turned into a political wedge. Bush and the Republicans used the issue in both the 2002 midterm election and the 2004 presidential election to help his and the GOP's cause.

In 2002, Republicans labeled then-Sen. Max Cleland, D-Ga., who had lost limbs in Vietnam, as weak in his defense of the homeland. Cleland lost his reelection bid. In 2004, even though opposition to the Iraq War was rising, Bush campaigned heavily on the theme that he would keep the country safe. To bring home the point, Republicans staged their national convention in New York, near the anniversary of 9/11.

With Democrats on the defensive in a military-infused political climate, the party scrambled to prove that their leaders had military bona fides. David Axelrod, who was Obama's chief political strategist, pointed to the 2004 Democratic convention that nominated then-Sen. John F. Kerry, a decorated Vietnam veteran, and said, "We essentially transformed our convention into a VFW meeting. That would not have happened if not for 9/11."

Then the politics of it all shifted. By the time of the 2008 election, Bush was highly unpopular, and the Democratic candidate who had opposed the Iraq War, Barack Obama, prevailed over other candidates who had supported the resolution authorizing Bush to launch the war, namely Hillary Clinton and Joe Biden.

The GOP nominee, McCain — a Vietnam prisoner of war and true war hero - was the strongest advocate for sending more troops into Iraq in 2007. He lost the 2008 presidential election. As vice president, Biden argued against a similar troop surge in Afghanistan.

If 9/11 could not sustain unity for long, there were other events that tested whether America could break out of its divisions. The financial crash of 2008-2009 is one, an event that crushed many families and that cried out for a united response. But Obama, whose election was hailed as a sign of racial progress, was able to produce not unity but more division: a tea party revolt, GOP obstruction in Congress and, worse, a rise in racial resentment among some White voters and outright racism among others.

As he was responding to the 9/11 attacks, Bush had sought to tamp down anger and rising hate crimes aimed at Muslim Americans, saying this was not a war against Islam. Donald Trump, as a candidate and as president, did the opposite, calling for banning the entry of all Muslims into the country (an announcement that coincided with the anniversary of the attack on Pearl Harbor).

Trump's campaign and presidency further exacerbated the existing racial tensions and divisions. Trump spread conspiracy theories about Muslims in New Jersey cheering the fall of the twin towers of the World Trade Center on 9/11 and about where Obama was born. He continues to spread other conspiracy theories today; they too have infected politics.

The coronavirus pandemic, when it hit U.S. shores in early 2020, amounted to the biggest threat to America since 9/11, a deadly virus in a globalized world that demanded a unity of purpose in response. Instead, it too has become a political conflict, over the wearing of masks and the administration of lifesaving vaccines. The 20th anniversary of the events that led to the invasion of Afghanistan finds the United States no longer in that conflict overseas but in a costly debate at home over how to wage a war against a virus.

The ceremonies commemorating 9/11 are wholly appropriate, designed to mark the loss of innocent lives and the selfless heroism of firefighters and police and other first responders who threw themselves into efforts to recuse anyone who could be rescued and to recover those who could not, and those on Flight 93 who gave their lives to save others. They remind all Americans of what is best about the country.

But it should also be noted that as the nation, and elected officials in Washington, hold these events, there is talk about reinstalling fencing around the Capitol in preparation for a rally next weekend in Washington in support of those arrested and jailed after the Jan. 6 attack on the Capitol. This time it is not international terrorism that poses the greatest threat to the homeland; it is domestic terrorism from white supremacists and others. Twenty years on from 9/11, that is the state of the country.