Image caption Karl Rove became one of the better-known advisers

It's the job of an adviser to be everything from a sounding board to a punchbag, writes Jonathan Powell, former chief of staff to Tony Blair.

President Obama's trip to Britain last week wasn't just a PR triumph for the 44th president of the US. It was an organisational triumph for his aides and advisers.

Every step of the way, from the "impromptu" game of table tennis with David Cameron to the Downing Street barbecue, would have been planned with meticulous care.

Planning, along with advising, consoling and bolstering, are key parts of the job of advising the world's political leaders.

But who are those aides lurking behind the president? And what does it take to become a trusted adviser?

The role of adviser is an odd one - you may find some of your finest words coming out of your boss's mouth but you can never take the credit. Jonathan Powell

I've spoken to the men who were closest to the 42nd and 43rd presidents of the US, Bill Clinton and George W Bush.

Karl Rove spotted the presidential potential of George W Bush almost from the first moment he met him. Rove was 22 and Bush was 26.

"In the front door of the Republic National Committee walked, a guy in his National Guard flight jacket, blue jeans, cowboy boots and more charisma than any human being should have," Rove recounts.

"I began to see, after he became governor of Texas that there was some real possibility and potential there, that he had enormous powers of leadership, big vision, and, as a manager of a large entity, a state government, he had very adroit skills and as a political manager, to manage problematic relationships, he had enormous smarts and an incredible reservoir of tools at his disposal."

What followed was a relationship which took Bush - and Rove - from Austin, Texas, to the White House.

Being president involves taking complex decisions. Josh Bolten, Bush's chief of staff, always tried to encourage others to be frank in front of the president.

Image caption One of Mike McCurry's jobs was to ask questions as the press would

"I took it as my role as chief of staff where an issue was truly presidential to insist that the disagreement be aired in front of the president in full glory.

"So I found myself in many meetings needling cabinet officers and senior advisers and prodding them into taking the extreme form of disagreement that I knew existed outside the room to give the president a real chance to make a decision, and for the boss that I served… to make hard decisions. If they're easy decisions they're not needed."

The role of trusted adviser becomes essential when your boss is immersed in a crisis.

And being a key aide can also involve dealing with your boss's mood swings.

Bill Clinton had a notorious temper, and during the stresses of the Monica Lewinsky saga his aides often bore the brunt of it.

It fell to Mike McCurry, Clinton's press secretary, to prepare his boss for aggressive questioning.

Find out more... The Men with the Ear of the President, presented by Jonathan Powell, is on Radio 4 at 2000 BST on Tuesday 31 May. Or catch up afterwards on iPlayer

"It was a standard technique of ours to prepare for a press conference, if we were going out to face the press that we would sit them down, usually with Vice-President Gore at his side, and really test him with the really negative questions he was likely to get from the press.

"I got the opportunity just to look Bill Clinton in the eye and ask him the most excruciatingly embarrassing questions that were going to pop up that day, and you could just see his face flush and get red and he'd shake his finger at me and say: 'Well that's the problem with you and your friends in the press, you're trying to destroy everything decent about this country.'"

And you may even need to tell your boss an embarrassing home truth, notes Bolten.

"I was at an event early in President Bush's tenure in which, in remarks before a large audience, he used the word 'misunderestimated'.

"Somebody had to tell him that he had said 'misunderestimated' and it's not a word. And, so he came off the stage and I said 'that was really good except you said misunderestimated' and he said 'no I didn't' and I said 'yes you did'. And he said 'no I didn't'.

Image caption Jonathan Powell spent 10 years as Tony Blair's chief of staff

"And then he looked around for confirmation to others who were hovering around and everybody was looking at their shoes."

When Rove started to go a little far with his boss, Bush would call him "turdflower", a West Texas flower that grows through a cowpat when it rains.

It was enough for the man dubbed "Bush's Brain" to realise he had gone too far.

The role of adviser is an odd one. You may find some of your finest words coming out of your boss's mouth but you can never take the credit. Most of the time you are in the shadows rather than the limelight, and you must always be on hand to take the blame when things go wrong.

The rewards are proximity to power, and the chance to influence policy in the most direct way. At its best you are a sounding board, at its worst, a punch bag. Some days both.

In other words, all power flows from the boss. And even the most expert political aide would do well to remember it.