The Orlando massacre - the deadliest shooting in US history - has reignited the debate about the country's gun laws.
President Obama branded the attack an "act of terror and hate"and urged Americans to decide whether this is the "kind of country we want to be".
But have his efforts have so far made any real progress?
- Why has Obama failed to tighten gun controls despite calling for them for years?
Many thought the Sandy Hook school massacre in Connecticut in December 2012 would be a tipping point.
Twenty children and six staff members were shot dead by Adam Lanza, 20, who opened fire after arming himself with weapons including a .223-calibre rifle and a Glock handgun.
The debate had been dormant until that point but the shock generated by the attack seemed to galvanise support for action, with demonstrations in favour and polls suggesting a shift in public opinion.
But those who imagined change was going to come underestimated the strength of America's gun lobby.
So more than three years and numerous school shootings later, President Obama has been left still making impassioned pleas for change.
- Why is the gun lobby so implacably opposed to change?
Self defence and security are among the arguments most regularly put forward. But the gun lobby's trump card is the US constitution.
The second amendment states: "A well- regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed."
Opponents argue that this was meant to apply to the 18th century militia, made up of citizen soldiers and a key element of the new nation's defence forces.
They argue it is inappropriate in the modern USA with its massive professional army.
But the courts have cited the amendment in upholding the right to bear arms in key rulings.
- Why is the gun lobby so powerful?
The main group, the National Rifle Association, describes itself as America's longest-standing civil rights organisation.
It claims to have more than five million members, or "proud defenders of history's patriots and diligent protectors of the Second Amendment". And it has proved itself to be a very powerful lobbying machine over the years.
- How easy is it to buy guns in the US?
Lots of shops, including the huge Walmart chain, sell guns. They can also be bought from gun shows or through private sales.
Background checks are only conducted with shop purchases when buyers have to fill out a form from the federal Bureau of Alcohol, Tobacco, Firearms and Explosives.
According to the Coalition To Stop Gun Violence, 40% of guns change hands in the US without a background check.
- So has the gun control lobby made any progress in the wake of all the massacres?
Some new restrictions have been introduced at state level.
And in August last year Walmart, the largest gun retailer in the US, announced it was to stop selling assault and sporting rifles.