Donald Trump will be simultaneously handed power to launch nuclear weapons as he is inaugurated tomorrow.
Here we explain how the “thin-skinned” and “impulsively tempered” President-elect can wield the power of the 'nuclear football' and what’s stopping him from using it.
When does he get the nuclear codes?
An unknown military aid will accompany President Barack Obama during the handover ceremony tomorrow. They will be carrying the briefcase which inside holds the digital piece of hardware, measuring 3in by 5in, known as “the biscuit”, and will pass it to Mr Trump’s side.
A briefing for the incoming president on how to activate them will have already taken place in private.
Cristina Varriale, a research analyst in proliferation and nuclear policy at the Royal United Services Institute (RUSI), told The Independent: “Right from the moment he is inaugurated and officially becomes the president of the United States, Trump will have access to the nuclear codes.”
What could stop him using it?
“In theory the president has full discretion over authorisation of nuclear use, however in practice, launch will still depend on other factors, including a human element," added Ms Varriale.
Mr Trump would make the decision first, but he would be giving permission to US Secretary of Defence, retired US Marine General James Mattis, to authorise the launch.
Mr Mattis could disobey the order but this would constitute mutiny and the president could fire him and turn to his deputy secretary of defence – and so on.
Also, under the 25th Amendment of the US Consitution, a vice-president could declare the President mentally incapable, but would need majority backing from cabinet.
Non-proliferation expert Mark Fitzpatrick, of the International Institute for Strategic Studies in Washington, also told BBC News: “There are no checks and balances on the president’s authority to launch a nuclear strike.
“But between the time he authorises one and the time it’s carried out there are other people involved.”
How the message is sent?
Inside the briefcase is a black book with a menu of strike options. He then authenticates his identity as commander-in-chief using a plastic card.
Once that’s done, the order is passed via the chairman of the Joint Chiefs of Staff, to the Pentagon war room, and then, using sealed authentication codes, to the US Strategic Command HQ in Offutt Airbase in Nebraska.
The order to fire is transmitted to launch crews using encrypted codes that have to match the codes locked inside their safes.
Less than an hour apparently. Land-based missile flight times between the US and Russia, or US and China, are around 30 minutes. That could be as little as 12 minutes from a submarine lurking in the Western Atlantic Ocean.
How much damage could do?
"The US still remains one of world’s nuclear superpowers – the other being Russia – with an arsenal that has the potential to be incredibly destructive and change the world as we know it,” said Ms Varriale.
As of September 2016, according to the BBC, America had 1,367 strategic nuclear warheads, Russia had 1,796, and the UK had 120.
Why would he use it?
Mr Trump has given mixed messages on nuclear weapons.
In March he said it was a “last resort”, in Mr Trump's interview with Michael Gove he said it should be “reduced very substantially”, but last month he tweeted the US must “expand its nuclear capability until such time as the world comes to its senses regarding nukes”.
President Harry Truman used two atomic bombs on Hiroshima and Nagasaki in Japan in 1945 to, by his justification, end the Second World War.
Ms Varriale added: “Although there are still many questions over Trump’s understanding of nuclear weapons, and how he see’s nuclear use, there would still need to be a number of significant steps before the prospect of intentional nuclear use by Trump becomes a near term possibility."
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies