Joe Biden's voice was full of emotion as he addressed the American people. "I'd hoped when I became president that I would not have to do this again," he began. "As a nation, we have to ask: 'When in God's name are we going to stand up to the gun lobby? When in God's name will we do what we all know in our gut needs to be done?'"

Biden was talking about the massacre at Robb Elementary School in Uvalde, Texas on Tuesday. The 18-year-old killer, armed with a handgun and a semi-automatic rifle, had shot his grandmother before attacking the school. He was shot dead by police.

It was the 27th school shooting in the US this year, and the worst primary-school attack since the Sandy HookThe killings at the Connecticut school were carried out by a 20-year-old using a semi-automatic rifle owned by his mother, whom he also killed. massacre in 2012. On that occasion, 20 children and 6 teachers were killed. According to recently released statistics, more American children and teenagers are killed by guns than by anything else - including car crashes.

"These kids weren't unlucky," said Chris Murphy, a Democratic Senator from Connecticut. "This only happens in this country. Nowhere else, nowhere else do little kids go to school thinking that they might be shot that day."

To the rest of the world, the problem is entirely obvious. It is ridiculously easy to buy incredibly powerful guns in the US.

But a large proportion of Americans do not see it that way. A recent poll found that 52% were in favour of tighter controls. Speaking in the Senate on Tuesday, Ted CruzA Senator who ran against Donald Trump for the Republican presidential nomination in 2016. declared that restricting the rights of "law-abiding citizens... doesn't work. It's not effective. It doesn't prevent crime."

To people like Cruz, gun ownership is a sacred legacy of the American War of IndependenceThe colonists' war against the British government lasted from 1775 until 1783.. The Second Amendment to the US Constitution, passed in 1791, rules that "A well-regulated MilitiaA military force made up of ordinary citizens rather than professional soldiers., being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed." 

After the American Civil WarA war fought from 1861 to 1865 between the slave states of the South and the free states of the North, after the former seceded from the Union., arms manufacturers left with surplus guns persuaded ordinary shops to sell them, and advertised guns as a way of giving boys "sturdy manliness". At the same time, armed groups sprang up both to protect newly freed slaves and to terrorise them.

For most of the 20th Century, there was widespread support for gun control. Gangster warfareCriminals such as Al Capone made ruthless use of guns. and political assassinations, such as that of President KennedyHe was shot dead in Dallas in 1963., inspired public revulsion.

But anxiety about rising crime rates led more people to buy guns for personal protection, rather than for hunting and target shooting. Between 1999 and 2015, the proportion of people buying them mainly for self-defence rose from 26% to 63%. Many states relaxed controls rather than tightening them. 

Lobbyists promoted the idea that even ordinary citizens needed military-style weapons. Conspiracy theorists suggested that they might need to use them against their own government.

Opinion is now divided largely along political lines. While 91% of Democrats support stricter controls, only 24% of Republicans do.

Yes: Every situation has a tipping point, and this is it. The US has a president committed to gun control, and after the latest tragedy, there will be enough public support to pass the necessary laws.

No: Politicians are too worried about losing gun owners' votes. Previous terrible incidents have not produced changes. Even if Biden could achieve new controls, the next president could reverse them.   

Or... So many Americans now own guns, and so many dies by suicide with them, that the manufacturers could run out of customers and start selling protection such as body armour instead. 

Sandy Hook - The killings at the Connecticut school were carried out by a 20-year-old using a semi-automatic rifle owned by his mother, whom he also killed.

Ted Cruz - A Senator who ran against Donald Trump for the Republican presidential nomination in 2016.

American War of Independence - The colonists' war against the British government lasted from 1775 until 1783.

Militia - A military force made up of ordinary citizens rather than professional soldiers.

American Civil War - A war fought from 1861 to 1865 between the slave states of the South and the free states of the North, after the former seceded from the Union.

Gangster warfare - Criminals such as Al Capone made ruthless use of guns.

President Kennedy - He was shot dead in Dallas in 1963.