By an accident of timing, I was reading the latest of Robert Caro’s vast books on Lyndon Johnson on a flight yesterday, and reached the point where President Kennedy was assassinated, and Johnson had to step up.

It is one of those books that makes you want a flight to go on and on, because it is so good, so well written, so well researched, and such a gripping story of power, politics and human drama.

The world was so consumed with the immediate aftermath of the assassination in Dallas, the grief, the arrests and murders which followed, the plans for three days of national mourning, that to some extent Johnson slipped into the background.

But what the book captures brilliantly is the scale of challenge greeting any President, and the scope of abilities needed to get anything done. Johnson had been a masterful Senate figure, but became at times a figure of ridicule as Vice President. He was tolerated but at times humiliated by the Kennedy clan, and loathed deeply by Bobby Kennedy.

Yet when the moment came for him to become President via a bullet rather than the ballot box, with none of the transition time new Presidents are given, he really did step up to the mark. He used the moment to gather his friends, draw near as many of his enemies as he could, and to tell all of them that he needed them more than they needed him, and the country needed both of them.

Even as the rituals of death were being undergone, Johnson was having to deal with difficult issues in Congress, and knew that his chances of re-election within a year depended on holding together the Democrats, which also meant retaining the Kennedy aura, whilst getting things done with the Republicans.

Barack Obama, in common with many, myself included, names Doris Kearns G0odwin’s book on Abraham Lincoln, Team of Rivals, as one of the best and most influential political books he has ever read. (Time magazine this week has a front cover profile of Daniel Day Lewis, whose performance of America’s greatest President is seemingly brilliant in the new Spielberg film, and will unleash a fresh wave of interest in Lincoln.) I don’t know if Obama has read the Caro series on Johnson – this is the fourth, and there will be another one in a few years – but he should definitely take a look at the chapters on the transition as he settles in for a second term.

The story will be familiar, but the detail is fascinating, a lot of it about the management of the big figures in other parts of the political battlefield. ‘The most powerful man in the world’ is the cliche that attaches itself to the election of an American President – (could be a woman next time?) – but very few of them feel like it, and though Obama will be a happy and relieved man today, he won’t feel so powerful when he confronts the economic, environmental and security challenges, and realises how much he is going to have to rely on people who tend not to share his politics.

In the excitement of victory, we can forgive him the ‘four more years’ tweet to announce victory, complete with the twitpic of him hugging Michelle. I would have preferred something in the ‘now we can get the job done’ area. But very quickly he is going to have to get down to a lot of pretty raw politics, and focus on some very big issues, with the message less about himself and more about the help he will need to deal with those issues.

A few weeks ago, I thought he was home and dry. But that first TV debate, complete with another rather jarring reference to the First Lady, which was more celeb than politician, and a bizarrely lacklustre performance which gave no real sense of why he wanted power, let Mitt Romney back into the game. In the end, it was closer than it should have been. But he won and that is the important thing, and now he has to build bridges where the campaign knocked them down.

Another interesting facet of the Johnson book is that shortly before the JFK assassination, there was a big debate going on about the inability of the US to deliver change as promised by Presidents. Kennedy was facing Congressional gridlock in relation to both the economy and civil rights. The debate was going so far as to say the entire political system needed a radical overhaul.

It was the way Johnson used the mood created by the killing, and applied his political skills learned in Congress, that finally led to progress which – who knows? – might not have come had Kennedy got back alive from Dallas that day.

Obama still has a lot of warmth and goodwill going for him. He still has huge charisma. He now has more experience than he had. But he also has a reputation for being a bit aloof and distant, including from people that now he has to court assiduously if anything is to be done. This was a great victory given the state of the economy, but not an overwhelming one, and he knows he has Hispanics, blacks, young people and women to thank for getting him over the line. He also has the Tea Party to  thank for leading Romney up the wrong strategic track, and leaving him too little time to get back where he should have been the whole way through.

Domestically, Obama has massive challenges, and as one US voter put it on the BBC News this morning ‘I wanted to give him four more years to do the things he said he would do in the first term.’ Internationally, he has big challenges and his international partners will probably be looking for a more co-operative and internationalist approach in the issues facing the world, where he has been so lucky to have Hillary Clinton doing the heavy lifting.

What emerged from JFK’s death was a new Johnson, or at least something closer to the old one before he became Number 2 in the White House rather than Number 1 in the Senate. What may emerge from this election is the same basic Obama, but with a new approach that is more outward looking. And I suspect he has already started down that road.

Finally, given we are talking about lessons from past Presidents, a word on the role in the campaign of Bill Clinton. He is still one of the great political communicators and one of the great campaigners of our times, and Obama owes a lot to him as well as to Hillary. I still wonder how the world might have been different if Al Gore has used Clinton properly in the campaign he lost to George W Bush in 2000.

The lesson of Lincoln, and the lesson of Johnson, is that you can get more done if you recognise power and talent where you see it, and use it as best you can. Obama will have to apply that right across the US political system now.