By Justin Webb
North America editor, BBC News
A few days ago, I was watching Tony Blair being interviewed on American television. The interviewer was one of the most able and well-informed of his breed.
Yet at the end of the five minutes even he could not escape this solecism: "Mr Prime Minister, thank you."
Mr Blair is of course, Mr Blair.
Hillary spent eight years in the White House as first lady
He has not been prime minister for some time. And yet in the American system, it feels terribly impolite not to hint at what once was.
There is only one American president, but all former presidents are correctly addressed as "Mr President."
So, at a diner in South Carolina, some time in the early part of this year, I found myself calling out across the counter: "Mr President, would you speak to the BBC?"
The president I was approaching - surrounded as always by hangers-on and security men - was Bill Clinton. He was affable.
That hugely expressive face - those eyes that had been darting across the audience he had just addressed - now focussed on some question I had about the campaign he was waging to get his wife into the White House.
Seconds later though, he flipped.
The sceptical view of Bill is that with Bill - or Mr President - it is all about Bill, and his presidency
Surrounded by local reporters on the way out of the diner, someone had annoyed him. The face flushed, the eyes hardened, the finger wagged.
I could see the commotion as he harangued his target, but I could not get close. The bear was being baited and everyone was desperate to see the sport.
This is the problem Mr Obama's White House now faces. Bill Clinton is box office.
He is still a mesmerising public speaker. For my money, he is actually much better than Mr Obama because he gets to the point quicker.
His Florida endorsement of Mr Obama, given late at night in a warm breeze, flags fluttering and crowds swaying, was electrifying.
Is the Clinton aura just an aura?
His star power could continue to assist Mr Obama's programme particularly abroad. But will it?
The sceptical view of Bill is that with Bill - or Mr President - it is all about Bill, and his presidency.
In the breeze in Florida he was giving it welly, because he wanted to remind everyone how wonderful he was.
And yet, the sceptics claim, he was not really wonderful.
They claim the Clinton aura is just an aura. That the truth is that the Clinton partnership is poisonous, to them, and the nation.
I have a friend who interviewed Mrs Clinton early in the campaign.
He went to her New York home and was shocked at how sterile it was - like a hotel room, he said, plush but characterless.
This - according to the critics - is the heart of the Clinton darkness. The marriage that appears to be wholly about convenience - nothing grounded, normal, recognisably human.
When Hillary moved into that New York house in January 2000, ready for her successful Senate campaign, her advisers worried that the pictures would look sad - Hillary alone.
So his schedule had to be re-arranged in order that he could pose with her at the door.
The two principals had not thought to go to the house together. This is not normal, the thinking goes.
But what shocks people is not that they do not get on, but that they do. Why?
And what does this political team achieve? Very little, is the charge. Except drama.
When he became president, Bill was compared to a dog, chasing cars in the street, who one day catches up with one. What then?
Mrs Clinton campaigned for Mr Obama after losing her bid for nomination
Did he really manage anything in those eight years, other than that dalliance with Monica Lewinsky, best described by one of his aides as frivolous, reckless and small.
The economic boom was huge and is remembered with real yearning now, but the argument goes that it was hardly his doing.
At one campaign event this year I heard the warm-up speaker claim that the Clinton time had been wonderful, because America had been at peace.
Well, America had not been attacked, or you could argue, it had been attacked - the World Trade Centre had been bombed and the USS Cole blown up - but had not done much about it.
And the departure from office of the "Billary" team was famously tawdry. They had to give back furniture that they had taken with them.
According to a biographer, in the run-up to Hillary taking up her Senate seat in 2001, her people collected gifts - phoning wealthy donors and asking for Faberge serving spoons, Spode vegetable dishes, or just cheques, $5,000 (£3,570) minimum.
This is the underside of Team Clinton.
And this is why, in Obamaland, some are wondering whether the boss has made his first blunder.
When the secretary of state announcement was made one of the television comedians said: "Hillary can concentrate on foreign affairs and Bill can go back to domestic ones".
And that is the point. This is a team effort. The problem is not her, the problem is not even him: the problem is them.
From Our Own Correspondent was broadcast on Saturday, 6 December, 2008 at 1130 GMT on BBC Radio 4. Please check the programme schedules for World Service transmission times.