Four years ago, Barack Obama pledged to address gun control. The president-elect's statement on urban policy included a commitment to permanently renew an expired ban on new assault weapons, curbs to limit the unregulated trade in weapons at gun shows, and greater powers for law enforcement agencies to trace guns and combat the illegal arms trade.
That statement has since disappeared from the president's website as many politicians on both sides of the aisle try and steer clear of an issue – gun control – they regard as toxic, in the face of an unrelenting campaign by the powerful pro-gun lobby group, the National Rifle Association, to scrap or ease existing laws.
Even as police pieced together the details of how James Holmes collected an array of weapons and thousands of rounds of ammunition in the weeks before he killed 12 and wounded scores in an Aurora cinema, politicians mostly sidestepped questions about the ease with which guns can be owned in the US.
Robert Spitzer, author of the Politics of Gun Control and chair of the political science department at State University of New York College at Cortland, said that even after the latest tragedy, he does not expect the issue to figure in the presidential election.
"After their expressions of condolences, you'll find the campaigns will turn back to their pre-existing agenda and it will almost certainly not include the gun issue," he said.
Politicians of both sides of the aisle have come down against greater gun control. The divide is often regional and cultural as much as political, with many Democrats unwilling to incur the wrath of constituents who regard defence of their right to own weapons as a litmus test of American values.
Yet the NRA has not had it all its own way. Assault weapons ban
The most significant piece of gun control legislation of recent years was the 1994 Federal Assault Weapons Ban. It barred the manufacture and import of an array semi-automatic weapons for use by civilians, including the AR-15 used by Holmes, which is modelled on the US army's M-16 automatic rifle, and AK-47s. The production of some other types of rapid-fire weapons for the civilian market, including some pistols and shotguns, was also stopped.
The law covered semi-automatic weapons, which require the trigger to be pulled each time a bullet is fired. Automatic weapons, which fire a stream of bullets by holding the trigger down, were already restricted.
The legislation also banned high-capacity magazines that feed large numbers of bullets to a gun. Critics said they enabled criminals to kill more people. The law limited magazines to a maximum of 10 bullets.
The legislation did not prevent the resale of guns manufactured before the ban, but it did eat into their availability, and some kinds of weapons began to command a premium.
However, the law had a built-in time limit of 10 years. In the furious arguments over its renewal, opponents of the ban said it had no discernible impact on crime levels. The Brady Centre to Prevent Gun Violence, named after the White House press secretary wounded in an assassination attempt against President Ronald Reagan in 1981, countered in a report that the assault weapons ban led to a significant drop in the number of such guns used in crime, although they were always only a fraction of the total.
In March, 2004 the US Senate blocked an extension of the assault weapons ban. Repeated efforts since then to renew it have failed.
They have been led by a congresswoman from New York, Carolyn McCarthy, whose husband was among six people shot dead by a gunman on a train in 1993. McCarthy introduced bills in 2003, 2005 and 2007, but none of them made it past the committee stage.
Five years ago, a Republican congressman, Mark Kirk, introduced legislation to renew the assault weapons ban with additional guns included. The bill had four Republican co-sponsors but also died in committee.
Ammunition
There are no federal restrictions on how much ammunition an individual can buy. In many states, bullets are sold on supermarket shelves alongside everyday household goods.
Bullets and shotgun shells can also be bought in bulk at a discount online from sites such as the Texas-based Ammunition to Go. It sells a large variety including incendiary ammunition, "less lethal ammo" and 12 Gauge "Rhodesian Jungle" shells.
Holmes ordered thousands of rounds for his assault rifle and hundreds of shells for the shotgun he fired from internet sites. Police said he also bought a bulletproof jacket from a website.
Federal law does not require a background check for people buying ammunition, and sellers are not legally obliged to report even large purchases of ammunition to the authorities. However, some states and cities do have restrictions. Los Angeles, for instance, requires a permit to buy ammunition.
Attempts in Congress to regulate internet sales of ammunition have failed in the face of NRA-backed opposition. Magazines
After the repeated failure of efforts to renew the assault weapons ban, some members of Congress pushed legislation specifically to restrict the size of magazines fitted to guns. Under the 1994 law, new magazines could not hold more than 10 bullets. But it remained legal to sell larger magazines that had been owned before the legislation kicked in, and they began to fetch a premium.
However, when the legislation fell away in 2004, it made it easier for Holmes to buy a drum magazine capable of holding about 100 bullets, which could be fired in less than two minutes. Attempts to force through a law in Congress specifically addressing the size of magazines for sale have failed in the face of resistance from both Republicans and Democrats.
Jared Loughner, who wounded Gabrielle Giffords and killed six other people in Arizona last year, including a nine-year-old girl and a federal judge, used a semi-automatic pistol fitted with a high-capacity magazine, both of which would have been restricted under the 1994 law.
States
Some states imposed their own restrictions on gun ownership. California has banned semi-automatic rifles since 1989. New York, Massachusetts and New Jersey ban magazines with a capacity of more than 10 bullets manufactured after 1994.
But many states do not require a licence to buy a gun, although federal law requires a background check.
Arizona has almost no restrictions. Gun licenses are not required, and concealed weapons may be carried without a permit. The laws of other states, such as Florida and Mississippi, are nearly as lax.
California, on the other hand, requires that all handgun serial numbers are logged at sale, bans the sale of assault weapons, and gives local police departments and councils authority over the issuing of permits to carry a concealed gun. New York state requires licences to own or carry a handgun, and has restrictions on assault weapons.
One battleground is over the right to carry a concealed weapon. The NRA would prefer that no permit be required, but where they are, it has been pressing strongly for them to be issued automatically to anyone who is not excluded because they have a serious criminal record.
The Brady Campaign said just such a policy in Washington state meant that the police had no choice but to issue a permit to Ian Stawicki to carry a concealed weapon, even though he had a long history of violence and mental illness. Stawicki then killed four people dead in a Seattle cafe and shot a mother in the head near her children's school.
Stawicki's own father had asked for his son's concealed carry licence to be revoked, but Washington state police said they did not have the authority to do so.
The NRA is campaigning for a federal law scrapping regulations in some states, including New York and California, which give the police the discretion to refuse a permit to carry a concealed weapon. Ironically, the NRA argues that concealed weapons permits are necessary for people to protect themselves from men such as Stawicki.
The lobby group is also pressing for a federal reciprocity law, forcing one state to recognise gun licences and concealed carry permits from another. If passed, that would mean that a person who could not obtain a licence to carry a hidden weapon in a state could still do so if he obtained a permit in another state.
Gun shows
The NRA is also campaigning to keep open a loophole that permits the private sale of weapons without background checks at gun shows. New York's mayor, Michael Bloomberg, last year presented video recorded at a gun show at which an undercover investigator was sold a gun even though he told the seller he could not possibly pass a federal background check.
Bloomberg said that many of those who describe themselves as private sellers at gun shows are, in fact, professional weapons dealers looking to get around the requirement to make background checks on buyers. In 2009, another investigation instigated by Bloomberg discovered a man who billed himself as a private seller at a gun show offering 800 weapons for sale.
"We have demonstrated how easy it is for anyone to buy a semiautomatic handgun and a high-capacity magazine, no questions asked," said Bloomberg.
Congress
The pro-gun lobby has successfully blocked other legislation in Congress and is challenging the Obama's administration's attempts to use administrative procedures to try to limit the sale of weapons to criminals and drug cartels.
In an effort to stem the flow of guns to Mexican drug cartels from states such as Texas, two Democratic party members of Congress last year sponsored legislation to make weapons trafficking a federal crime. It has widespread support among police officers including the Federal Law Enforcement Officers Association which represents more than 26,000 federal agents.
But the legislation is facing resistance from the NRA, which has portrayed it as a step toward the government confiscating all weapons.
The NRA is also fighting a legal action against a move by the Obama administration to require gun shops in the four US states bordering Mexico to report if the same person buys two or more assault rifles and some other guns over a five day period. The pro-gun lobby pressed Congress to block the measure and the House of Representatives responded with a vote in favour of the NRA's position, although it had no legal effect.