Five years later, the 2001 terrorist attacks on the United States continue to have a far-reaching impact on national politics.
Hours after the attacks on September 11, 2001, members of Congress gathered on the steps of the Capitol building in a rare display of bipartisan unity to sing "God Bless America."
But in the five years since the 9/11 attacks, political differences within the country seem to have sharpened, especially over the war in Iraq.
With congressional elections looming in November, President Bush is refocusing national attention on the threat of terrorism on the five-year anniversary of the 9/11 attacks.
"We are fighting for our way of life and our ability to live in freedom," said Mr. Bush. "We are fighting for the cause of humanity against those who seek to impose the darkness of tyranny and terror upon the entire world."
Opposition Democrats largely supported the Bush administration's military campaign against al-Qaida and the Taleban in Afghanistan, immediately after the terrorist attacks. Many Democrats also voted to authorize the use of military force prior to the Iraq war, based on the president's contention that Iraq was developing weapons of mass destruction.
But the continuing bloodshed and difficulties in Iraq have taken a toll on support for the war in public opinion polls, and many Democrats have now broken with the president, and believe the Iraq effort is going in the wrong direction.
Retired Army General Wesley Clark is a leading Democratic critic of the president's handling of Iraq.
"Invading Iraq was an unnecessary war," said General Clark. "It distracted us from what we were trying to accomplish in Afghanistan, and it has been counterproductive in winning the war on terror."
The political divide over Iraq is the latest example of how the country is sharply polarized on a range of issues, from immigration to abortion to homosexual marriage. It also stems from the hard-fought 2000 presidential election, in which Mr. Bush narrowly defeated Democrat Al Gore.
Opinion polls suggest Democrats might be in a position to retake control of one or both chambers of Congress in the November elections. Both have have been controlled by Republicans since 1994.
Experts say this fierce competition for voters is sharpening the political divide.
Thomas Mann is a political scholar at the Brookings Institution in Washington.
"We have talked about the ideological polarization of the parties, but the other important factor is parity. That is, that they are so evenly balanced now, narrow majorities. That means almost a desperation on both sides to either hold or gain majority status," said Mr. Mann.
Experts say there is plenty of blame to go around for the quick evaporation of bipartisanship following the 2001 attacks, with the war in Iraq as the major flashpoint.
Lawrence Korb was an assistant secretary of defense during the Reagan administration and now is a foreign policy and defense analyst at the Center for American Progress in Washington.
"I think the real thing that created this partisanship was that the president deliberately, or inadvertently, or incompetently gave us the wrong reasons for going into Iraq, and those who tried to raise questions about that were considered weak or unpatriotic," he explained.
Others put more responsibility on congressional Democrats.
Danielle Pletka is an expert on foreign and defense policy at the American Enterprise Institute in Washington.
"I think it is enormously unfortunate on foreign policy to see the kind of venomous attacks that we have seen on Iraq, on Iran and a variety of issues, in the Congress, and from others," she said. "But at the end of the day, it should be very clear that politics is a market like everything else. If the people are not interested in tolerating violent partisanship, then they will not put up with it."
President Bush's public approval ratings have suffered over the past two years, in large part because of dissatisfaction with the Iraq war and with the administration's response to the devastation wrought by Hurricane Katrina last year.
But the president and his Republican supporters in Congress running for re-election are pinning their political hopes on the long-standing public perception that they would do a better job than the Democrats of prosecuting the war on terror.
David Rohde is a political expert at Duke University in North Carolina.
"The Republicans are going to focus on the war on terror, and Democrats are going to focus on everything else. The only issue on which the Republicans have an advantage is terror," he said.
Analysts point out that President Bush and the Republicans have used the terror argument to good effect in the two other elections since the 9/11 attacks, the 2002 congressional elections and Mr. Bush's re-election campaign in 2004.
Whether than happens again in 2006 will depend on what issues the voters deem most important.
Chuck Todd is editor of the Hotline political newsletter.
"If the voter goes into the polls thinking about Iraq, then Democrats will have a big night," he said. "If voters are going to the polls and thinking about terrorism, then Republicans have a fighting chance."
Opinion polls suggest many Americans would like to bring back some of the bipartisan national unity evident in the days following the September 11 attacks.
But political experts say that is unlikely anytime soon, given the fierce competition between the parties for control of Congress in November and a wide-open race for president in 2008.