What will be Trump's impact on the world?

Americans have long been proud of the peaceful transition of power at the heart of their political system.

They believe their form of government is not only the best way of running their own country, but also an example to the world.

That belief has taken quite a knock this year, with an election tainted by scandal that has undermined the standing of western democracy.

Donald Trump assumes office with a cloud of controversy and doubt surrounding him.

Questions linger about the impact of Russian hacking on the electoral process, and the suspicion remains he has somehow been personally compromised by Russian intelligence.

Ethics experts and officials say his failure to produce tax returns is unacceptable and his attempts to remove himself from his businesses inadequate.

The Trump transition process caused deep concerns because of differences between Mr Trump and the people he wants in his cabinet, particularly on how to handle Russia.

While he talks of striking a bargain with Vladimir Putin, his nominees say the Russian leader is trying to break NATO and may need to be confronted.

Anthony Arend, professor of government and foreign service at Georgetown University, told Sky News that this is unprecedented and potentially dangerous.

"It confuses the allies and I would say also emboldens our adversaries if there seems to be some kind of confusion about what's going on in the United States - the cabinet's saying one thing, the President is saying something else and Congress is moving in a different direction.

"That's a perfect opportunity for Putin to take advantage of that and undertake some kind of adventurous activity."

On the campaign trail and in interviews before his inauguration, Mr Trump caused deep concern by calling NATO obsolete, writing off the EU and disparaging close allies.

Traditionally, incoming presidents reassure friends and unsettle potential enemies. Donald Trump upended the foreign policy playbook by doing the opposite.

Professor Daniel Nexon, foreign relations scholar, says that is deeply worrying.

"I don't think I've ever had so much personal anxiety about the fate of basic institutions that have served the United States and its allies extremely well since the end of the Second World War and certainly since the end of the Cold War."

For seven decades, America has led efforts to build a world order guaranteeing security and stability. For the first time the US President seems prepared to withdraw from that.

It seems the new leader of the free world has little respect for some of the foundations of that free world, leaving Washington's foreign policy establishment in a state of considerable anxiety.

Watch live coverage of inauguration day on Sky News. Adam Boulton is in the US presenting a special Sky News programme - Trump: America's President - at midnight tonight.