For three decades, the story of gun control was one of notorious crimes and laws passed in response, beginning with the federal law that followed the assassinations of Robert F. Kennedy and Dr. Martin Luther King Jr. in 1968. But after a Democratic-controlled Congress in 1994 passed bills proposed by President Clinton to restrict certain kinds of assault weapons and to create a national system of background checks for gun purchases, the political pendulum began to swing the other way. President Bush’s defeat of Al Gore in the 2000 presidential election was attributed in part to the perception among gun owners that Mr. Gore was “anti-gun.”

Supporters of gun control regularly point to the power of the National Rifle Association, whose 4.3 million members make it one of the most effective advocacy groups in Washington.

In 2008, the Supreme Court ruled that the Bill of Rights included a guarantee of the personal right to own a gun. The decision was both a measure of how far the pro-gun debate had moved, and a blow to many of the stricter gun control laws adopted by cities like Washington and Chicago.

In recent years, there have been calls for a renewed debate over gun violence after a series of horrific shootings. In November 2009, an Army psychiatrist at Fort Hood, Tex., was accused of shooting and killing 13 people and wounding 30 people. In January 2011, a gunman in Tucson, Ariz., armed with a Glock semiautomatic, shot and killed six people and wounded 14 others, including former Representative Gabrielle Giffords, Democrat of Arizona.

In the wake of the Tucson shootings, gun control advocates said they believed the shock of the attack would alter the political atmosphere, in no small part because one of the victims was a member of Congress. But the bills that were introduced — including ones to restrict sales of 100-bullet magazines or to tighten background checks — went nowhere.

Calls for a Renewed Debate After Colorado Rampage

The frustration of gun-control proponents was even more clearly on display in the wake of a deadly rampage in July 2012, when a gunman in Aurora, Colo. — armed with an AR-15 assault rifle, a Remington 12-gauge shotgun and a 40-caliber Glock handgun — opened fire in a crowded theater at a midnight showing of the latest Batman movie, killing 12 people and wounding 58 others. The victims included members of the military and a 6-year-old girl. The attack was one of the deadliest mass shootings in the history of the United States.

In response to the tragic shootings, Mayor Michael Bloomberg of New York called on the presidential nominees Barack Obama and Mitt Romney to come up with a comprehensive gun control policy.

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