What is it about Barack Obama that everything in life seems to come so quickly to him? For almost all the other American presidents, getting to swear the oath of office for a second time is the consuming ambition of their careers. It means that they have succeeded where many others have failed, and been re-elected to serve a second term in the White House.

President Obama has already been sworn in twice and it's only day three of his presidency.

Of course, this repeat performance was the consequence of a mistake, not success. On Tuesday in front of a mere two million people in Washington and hundreds of millions around the world, the US Chief Justice, John Roberts, and Mr Obama tripped over each other like a couple of workmen delivering a piano and the result was that the words of the presidential oath were spoken in the wrong order.

So on Wednesday evening, out of an “abundance of caution”, the two men repeated the exercise in the White House.

Why bother? Wouldn't it be just a few wacko conspiracy theorists and constitutional trainspotters who would insist that there was something illegitimate about an obviously legitimate president? Perhaps. But the fact is, the words of the oath are in the Constitution. The sacred document says of the president: “before he enter on the Execution of his Office, he shall take the following Oath”, and then gives the precise words, in order.

Some clever lawyer was undoubtedly already preparing a brief that would argue that all the executive decisions made by Mr Obama would be null and void because he had not complied with this constitutional requirement. At the very least it would have occupied White House lawyers with such nonsense for years. So wise counsel dictated a do-over.

Oddly enough, for such a linguistically gifted man, it wasn't the only flub in the new President's first moments in office. He began his inaugural address by noting: “Forty-four Americans have now taken the presidential oath”.

That's inaccurate. It is true that Mr Obama is officially the 44th president. But, as every schoolgirl knows (it was my 12-year old daughter who pointed it out to me), for some odd reason, Americans number their presidents by terms of office served consecutively.

Grover Cleveland, the only man to have served two non-consecutive terms, is thus counted twice - as both the 22nd and 24th. So, in fact, only 43 Americans have now taken the oath.

Two gaffes in Mr Obama's first four minutes as president. Do you miss George Bush yet?

Verbal infelicities aside, Mr Obama has started his presidency in good shape, helped in large part by a paradox.

He presides over what must be the worst set of conditions that have confronted a US president at least since Ronald Reagan came to office in 1981. But he sets out with a reservoir of goodwill, at home and around the world, on a scale that no president has had since Dwight Eisenhower.

As far as I can make out, the gap between the final opinion poll approval ratings for President Bush and the ratings for Mr Obama as he moved into the White House was the largest since Dwight Eisenhower took over from Harry Truman in 1953. A mood of distinctly un-American pessimism dominates. It is alleviated only by a genuine sense, among all but a few sore-loser Republicans, that this bright, exciting new president offers a real chance of renewal.

This means, that, contrary to what everybody (myself included) has been saying, Mr Obama is not, in fact, burdened with excessive expectations. Hopes for Mr Obama are certainly high. But expectations - a very different matter - are actually quite low.

Polls suggest that people think it will take years for the economy to recover. There is a strong sense that since the new man is not responsible for the mess left by the old one, he should be given time to fix it.

What is more, Mr Obama has shown a pleasing pragmatism in his appointments and early pronouncements. He seems to be guided by the principle that government should do what works, not what some rhetoric uttered in a campaign speech dictates. This will serve him well, and if he's genuine about ending tired partisanship, he will be well on the road to sainthood.

But, amid all the goodwill and excitement, let me, in this, my farewell column, play devil's advocate and identify what I think are the three biggest dangers to a successful presidency.

The first is, despite the low expectations, the economy. People will give Mr Obama time but eventually they will expect results. He and the country are staking much on his economic stimulus plan. If it works, in good old-fashioned Keynesian style, Mr Obama is home free.

But what if, as a number of economists fear, it doesn't work, either because it is insufficient or because somehow the structural deficiencies in the US economy won't respond to traditional demand management? Mr Obama's enlightened pragmatism will surely be tested.

The second is terrorism. The one piece of credit that the American people still allow Mr Bush is that, after 9/11, he kept the country safe.

If, God forbid, there should be an attack on Mr Obama's watch, we can expect the initial reaction to be an outpouring of national unity. But quite quickly, Republicans will turn on the President, and so might the people. They will point to yesterday's orders by Mr Obama to close closing Guantánamo Bay and ban coercive interrogation techniques - applauded around the world - as critical errors that softened up America's defences.

Americans may well discover that it's all very well to be liked again, but they would sooner be safe in their homes, offices and shopping malls.

The third danger is Congress. The Democrats in control there are delighted to go along with Mr Obama for now. But at some point, especially if the economy does recover, Mr Obama is going to have to ask Congress to make sacrifices in spending programmes to get the budget under control. That could prove bloody.

Given the exigencies of the presidential election timetable, I would say that Mr Obama has about three years to navigate these waters. There will be no shortage of alternative captains if he struggles.

On the other hand, if he can keep America safe, engineer the beginnings of recovery and face down his erstwhile allies in Congress, he will get the extremely rare privilege of taking that oath of office for a third time.

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