The Arizona shootingOn January 8, Democratic Rep. Gabrielle Giffords was hosting a "Congress at your corner" event in a grocery store parking lot in Tucson, Arizona, when a gunman open fire.
The suspect, 22-year-old Jared Loughner, shot 19 people. Six people were killed, including U.S. District Court Judge John Roll and Gabriel Zimmerman, a member of Giffords' staff. Miraculously, the Arizona congresswoman survived after being shot in the head at point-blank range.
The assassination attempt stunned the nation and the world and prompted discussions on everything from the lack of bipartisanship in Washington to gun control and mental health issues.
Wisconsin protestsAfter Wisconsin's Republican Gov. Scott Walker signed a law in March that nearly eliminated public workers' collective bargaining rights, thousands of protesters took to the streets and invaded the state capitol building.
The controversial law prompted weeks of protests and spurred unprecedented recall efforts. Backlash against Republican efforts to roll back union rights spread to other states.
War in LibyaIn March, U.S. and NATO forces began airstrikes to support a rebel uprising against Libyan strongman Muammar Qaddafi. After months of fighting, the rebels overtook the capital of Tripoli in August, pushing Qaddafi into exile.
Qaddafi himself was killed as Libyan rebel forces battled for control in his hometown of Sirte on October 20, liberating the Libyan people from decades of oppression.
Qaddafi's defeat was a victory for President Obama, who led NATO forces in assisting the Libyan rebels. But with the seven-month civil war over, Libya now faces the task of building its future without resorting to the same tactics that paralyzed the nation for decades.
Government shutdown averted, barelyWhat once might have been unthinkable became a common theme in 2011 -- the threat of a government shutdown.
Congressional gridlock brought the federal government to the brink of a partial shutdown on multiple occasions this year -- including in March, April, September and December. Yet in each instance, Republicans and Democrats managed to reach an agreement at the last minute, brokering deals to keep the government funded at least temporarily.
In this picture, House Speaker John Boehner announces that a deal has been reached to avert a government shutdown on April 8.
Donald Trump and Obama's birth certificateBillionaire businessman Donald Trump coyly suggested all year that he could jump into the 2012 presidential race. He also promoted the baseless suspicion that President Obama was not born in the United States.
Trump managed to bring enough attention to the "birther" claims that Mr. Obama was compelled to release his long-form birth certificate from Hawaii in April. As he did however, the president condemned the media for paying attention to "sideshows and carnival barkers."
Osama bin Laden killedAl Qaeda leader Osama bin Laden was shot dead deep inside Pakistan in a night-time helicopter raid by U.S. covert forces, ending a decade-long manhunt for the mastermind of the September 11 attacks.
"Justice has been done," President Obama declared in a televised address (picture at left), sparking raucous celebrations across the United States and boosting the president's national security credentials in polls.
Schwarzenegger scandalOn May 16, days after former California governor and actor Arnold Schwarzenegger announced he was splitting from his wife Maria Shriver, he admitted to fathering a child 14 years earlier with a member of their household staff.
2012 GOP primary campaign takes offThe 2012 primary campaign was in full gear as summer rolled around and candidates officially jumped into the race. The race has proved remarkably fluid, with candidates rising to the top of the polls -- and then slipping back -- on a regular basis. While Mitt Romney (at left) has consistently stayed near the top of the polls, he's been joined there by Newt Gingrich, Michele Bachmann, Rick Perry, Herman Cain and Ron Paul. Meanwhile, candidates such as Jon Huntsman and Rick Santorum have failed to gain much traction in the race so far. Cain and Tim Pawlenty dropped out before the voting began, and several potential candidates such as Chris Christie, Mitch Daniels, Haley Barbour, Sarah Palin and Donald Trump decided against running.
Special report: Election 2012
Sarah Palin's bus tourSarah Palin's embarked on the "One Nation" bus tour in late May, visiting historic sites and American landmarks from Washington to Massachusetts. Here, her bus leaves the Liberty Bell Center in Philadelphia, Pennsylvania. Later in the summer, she visited Iowa and other stops in the Midwest. While the tour sparked rumors that the former Alaska governor and 2008 Republican vice presidential nominee was planning to jump into the 2012 race, Palin announced in October that she wouldn't be launching a campaign.
John Edwards indictedOn June 3, John Edwards was indicted by a federal grand jury on six felony charges that he solicited and used campaign contributions to hide his mistress and their baby.
The indictment is the culmination of a federal investigation that lasted more than two years and scoured through virtually every corner of Edwards' political career.
The former Democratic senator and former presidential candidate pleaded not guilty. He is set to face trial next year.
Anthony Weiner resigns in disgraceOn June 16, Rep. Anthony Weiner of New York resigned from Congress following the revelation that he had sent lewd photos and messages to several women he met online -- and then lied about it.
The seven-term Democrat was well known as an outspoken liberal, but his sexting scandal served as a warning to lawmakers of the dangers of imprudently using technology.
Debt ceiling showdownThe U.S. Congress has raised the nation's borrowing limit, or debt ceiling dozens of times without controversy. But in 2011, Republicans were determined to take a stand against Washington spending.
The GOP-led House drew out negotiations over raising the debt ceiling, bringing the Treasury Department to the brink of exhausting its borrowing authority. But in return, they managed to win a bill that would cut government spending by trillions over 10 years.
Here, Senate Majority Leader Harry Reid addresses the media after voting on the debt limit bill August 2. Just days later, on August 5, the credit rating agency Standard & Poor's downgraded the U.S. government's credit rating for the first time in the country's history.
Bachmann wins Iowa straw pollIn August, Michele Bachmann narrowly defeated Ron Paul to win the Iowa straw poll and position herself as a frontrunner for the Republican presidential nomination. (Tim Pawlenty's third place finish prompted him to leave the race.) Texas governor Rick Perry's entry into the race on the same day, however, lessened the impact of Bachmann's win, and she saw her standings in the polls slide after her summer triumph.
Obama introduces the American Jobs ActAfter watching the economy sputter all year, President Obama on September 8 went before Congress to propose another large round of stimulus -- $447 billion in spending and tax cut initiatives he dubbed the "American Jobs Act."
The president's supporters were impressed with the size of the plan and the president's bold rhetoric -- he repeatedly called on Congress to "pass this bill." However, Republicans decried the measure as wasteful and ineffective, and the package went nowhere.
While the bulk of the president's plans were left on the drawing board, the bill has served as a tool for Mr. Obama as he tries to compare his vision for America with the Republican vision.
10th anniversary of 9/11This year marked the tenth anniversary of the September 11, 2001 terrorist attacks, which resulted in the deaths of nearly 3,000 people after two hijacked planes crashed into the World Trade Center, one into the Pentagon in Arlington, Virginia, and one crash-landed in Shanksville, Pennsylvania.
In this picture, Nancy Gregory hugs her sons Carl, left, and Gregory as they pay their respects to her husband, firefighter Ken Kumpel, at the National 9/11 Memorial at the World Trade Center site in New York.
"Don't Ask Don't Tell" endsAfter 18 years, the contentious "don't ask, don't tell" policy, which barred gays and lesbians serving openly in the military, came to an end on September 20.
In this picture, local leaders and former members of the military hold a banner during a news conference marking the end of DADT in San Francisco, California.
Occupy Wall StreetWhat started with a few tents set up in New York City
CBS News/National Journal debateCBS News and National Journal held the first Republican presidential primary debate on broadcast television November 12.
The debate focused on foreign policy, and it took place in South Carolina -- a critical primary state.
Full coverage of the debate
Supercommittee failsAfter the contentious debt ceiling debate, Congress agreed in August to allow a bipartisan "supercommittee" of 12 congressmen come up with a plan to find an extra $1.2 trillion in budget savings.
Those three House Democrats, three House Republicans, three Senate Democrats and three Senate Republicans acknowledged that finding common ground by Thanksgiving was a lofty goal -- but they expressed optimism.
But despite hundreds of hours of closed door meetings, the committee failed to reach its goal, kicking into effect $1.2 trillion of automatic spending cuts. Some lawmakers, however, are now talking about rolling back those budget cuts.
In this picture, Sen. Jon Kyl, R-Ariz., a member of the supercommittee, talks with reporters outside his office in the Capitol on November 19.
Herman Cain bows outPizza magnate Herman Cain surged to the top of the Republican presidential field in the fall of 2011, after winning over conservatives with his "999" tax plan and his affable demeanor.
His campaign began to falter, however, after it was revealed that multiple women had accused the former restaurant lobbyist of sexual harassment. Additionally, Cain was charged with having a 13-year-long extramarital affair. Those allegations, on top of a few political gaffes that raised questions about Cain's credentials, finally forced Cain to suspend his campaign on December 3.
Flaws in Operation Fast and Furious exposedIn the operation known as Fast and Furious, the Bureau of Alcohol Tobacco & Firearms secretly encouraged gun dealers to sell to suspected traffickers for Mexican drug cartels to go after the "big fish." But ATF whistleblowers told CBS News and Congress it was a dangerous practice called "gunwalking," and it put thousands of weapons on the street. Many were used in violent crimes in Mexico.
The issue came to a head following the December 2010 death of border patrol agent Brian Terry, who was gunned down in Arizona near the Mexican border by illegal immigrants armed with weapons from the operation. Terry's killing touched off a firestorm that crossed international borders and triggered investigations, congressional hearings, denials and admissions to the upper levels of the Justice Department.
On December 8, U.S. Attorney General Eric Holder appeared at a hearing of the House Judiciary Committee to answer questions about Fast and Furious.
See more coverage of Fast and Furious from CBS News Investigative Correspondent Sharyl Attkisson
Iraq troop withdrawalThe last U.S. troops left Iraq in December, bringing an end to the nearly nine-year war that cost nearly 4,500 American and well more than 100,000 Iraqi lives and $800 billion from the U.S. Treasury.
In this photo, U.S. Army soldiers line their armored vehicles up as they prepare to turn them in the day after exiting service in Iraq on December 8 at Camp Virginia, near Kuwait City, Kuwait.