A MAN in uniform will wait discreetly behind the scenes at today’s United States presidential inauguration. He will carry the briefcase containing the codes with which Donald Trump will be empowered to launch the world’s most potent nuclear arsenal. For the next four years, a military aide with the briefcase will stay constantly by Mr Trump’s side.

It is a scary prospect, and not just because the reality TV-star businessman President has no experience of either politics or the military. Mr Trump has an erratic and volatile personality. He is thin-skinned, quick-tempered, and prone to vindictive retaliation, to judge from his juvenile use of Twitter. He is a man with poor control of his impulses.

Throughout the presidential campaign, commentators predicted that he would at some point drop the coarse vulgar braggadocio with which he sought to enlist the country’s disenfranchised angry white voters, and become “presidential”. He never did. Instead, he issued wild threats to deport 11 million illegal immigrants, ban Muslims from entering the United States, denigrate climate change, cosy up to the Russians, disparage NATO, and slap trade tariffs as high as 35 per cent on goods entering the US, starting a trade war that could plunge the world into recession.

But the signals from his team are mixed. He has nominated an Energy Secretary, Rick Perry, who thinks that the Department of Energy should not exist; a Secretary of State, Rex Tillerson, who has a history of doing commercial deals in Russia; and a Secretary of Defense, General James Mattis, who has been nicknamed “Mad Dog”. His chief Middle East adviser — his son-in-law, Jared Kushner — backs the extremist Israeli desire to abandon a two-state solution and suppress the Palestinian dispossessed.

Appearing before select committees in Congress, however, his nominees have sprung surprises. Mr Tillerson told the Senate Committee on Foreign Relations last week that the US was “not likely to ever be friends” with Russia: “At this point, they are in the ‘unfriendly adversary’ category.” And General Mattis has contradicted Mr Trump’s verdict that NATO is “obsolete”, and has called it “the most successful military alliance in modern world history”.

Trump nominees also rejected their leader’s insistence that President Obama’s nuclear-arms deal with Iran should be torn up. They said “no” to the idea that the US should withdraw from the Paris climate agreement. And the man chosen to be the new director of the CIA, Mike Pompeo, said that he would refuse to carry out an order from Mr Trump to torture suspected terrorists.

It is just possible that these men will be able to moderate the worst impulses of the new President. After all, Mr Trump lacks consistent views on many things — he has changed his mind about abortion and gay rights, for example — and seems inclined to go for whatever is politically opportune.

In ancient Rome, as victorious generals made their triumphal progress through the city, they were said to have a slave stand behind them in their chariots to whisper into the great man’s ear that this glory was transient, and that one day he, too, would die.

We can only hope that the presence of the man with the briefcase exercises a similar psychological restraint on Mr Trump.