I've been inside the "Bubble", the bubble that bobs behind the "Beast", floats after Potus. Potus is, of course, President of the United States, the "Beast" his armoured car, and the "Bubble" contains the journalists who are following him.
Many live much of their lives within the bubble but for me this is a first. I suppose I've been bubbled with Tony Blair, Gordon Brown and European Commission President Jose Manuel Barroso, but we don't use that term at home, and it's not quite the same enclosed experience.
The bubble takes many guises.
In New York, covering the United Nations meetings, the bubble feels like an emergency schoolroom set up in a grand mansion after some natural disaster: it is, in fact, in a sideroom of the city's grandest of the grand hotels, the very place where the UK prime minister and the US president walked and talked through the kitchens.
Underneath obese chandeliers dripping with glass pendants, narrow trestle tables are set up in neat ranks, three people to a table. Amid the gilt, wires trail and cables curl between our legs, the atmosphere hushed apart from the tip-tap clatter of 30 laptops, broken occasionally by the need to file. No studios these days, just microphones.
"John, the president needs the support of the Senate on this one... In New York today the president declared that America will roll up its sleeves and get to work... matching the commitment..."
There is an attempt to recreate home: like the White House briefing room, there is a small podium backed by a blue velvet curtain. And that podium is what it is all about.
Why bother with the bubble? The buzz and the brief... In return for a pose of passes, you get through security quicker, get to stay and be where the action is. But its real worth is on stories like the revelation of the secret Iranian base under a mountain.
It didn't feel like a privilege to get a late-night email warning the buses would be leaving at 0630. It did when we were told it was for a special statement by the president. The buzz on the bus that David... which bus is David on... had the story and had filed it at 0430... officials quickly confirm... the details are all true... we can go with it.
What has amazed me as an old political hand, is the quality, frequency and variety of background briefings: senior administration officials means just that - not some bloke in the press office. I can't go into details, of course, but one recent briefing blew my socks off: five of the most important advisers on a critical policy area in the same room, earnestly explaining what they're up to.
But there's much to learn. In my first two such briefings, I unwittingly breached bubble etiquette. When I ask a question, I preface it, "Mark Mardell from the BBC". Sometimes there is an element of theatre for the cameras about this, but in Britain and Europe it is considered a discourtesy not to tell a politician who you are and where you're from; it sounds as if they should know who you are and where you are from. Here, my producer whispers afterwards, it's not the American way, it's considered rather rude grandstanding to introduce yourself.
The big question: how close to the man do you get? Well, on this trip about 20 feet away, as he made his Iran statement. On Downing Street excursions, you'll be on the same plane as the PM and - unless he's feeling grumpy - he'll wander back into steerage for a chat. Here the president and Flotus (the First Lady of the United States)are on a different plane, probably in both senses of the word. Still I live in hope.
But every footstep of the president is observed and reported for the rest of us: in the heart of the bubble there is a pool. The pool are the rotated senior correspondents who go with the president when space is too limited to admit a seething gaggle, even a pretty select seething gaggle.
Their reports, at best, are witty and pithy, quickly emailed to all our mobile devices for instant insertion into what we are writing. But they are under such intense pressure to file instantly that sometimes purple prose collides with jargon, wrapped in an eagerness to excuse shortcomings.
Sometimes the result is a mournful haiku - I dream one up that goes:
"Potus and Flotus deplaned onto a verdant lawn. He touched her shoulder. Perhaps twice, my view obscured by an unfamiliar flag..."
While it is a privilege to be in the bubble, there is a danger: while we reporters like to see ourselves as ruggedly resourceful, on a trips like this, you can be as dependant as a small child, shepherded from bus to press room... eagerly sucking on the source. As our hapless bus driver drove, utterly clueless, around the empty streets of Pittsburgh, it struck me that it's a poor fate being a sheep if the shepherd is lost.
As we made another pathetic attempt to get down to a narrow street, I looked down on the streets largely emptied of people, kept outside the security cordon. There were a few lingering along the route who looked ready to cheer or boo. I don't know which. I couldn't talk to them.
The bubble's home is Washington. DC itself is a bubble, people who have lived there a long time will tell you with some truth and some self-deprecation that, at heart, it is a small southern city. The real city is pretty relaxed, but inside what most people MEAN by Washington - it seems to me at least as a very recent newcomer - there is an emphasis on personal contact, hierarchy and formality that feels curiously old-fashioned by European or British standards, and an obsession with process and policy that sometimes finds insiders talking about "the people" as an unreal abstraction they've never met.
So I must, somehow, be in the bubble but not of the bubble. Perhaps, I should try my hand at a haiku:
Reflections of the world cover the surface of the bubble
I cannot see them from the inside, looking out.
To do that I must deplane.
Swim outside the pool.
On second thoughts, I'll stick to reporting... where the devilish instinct is to pop any bubble you come across.
If you'd prefer to listen rather than read, head over to this week's edition of From Our Own Correspondent.