Political assumptions can remain constant for long periods and then change very quickly. And so they have in approximately 10 days since the publication of Senator Barack Obama’s book The Audacity of Hope. In the brief time he has been on a book tour, Mr Obama has overthrown much of the reigning conventional wisdom about what is likely to happen in the 2008 US presidential campaign, how shrewd politicians ought to behave and what the informal rules of the American system really are. Consider the following statements thought true by the political class in early October, but called into serious question by month’s end.

Hillary Clinton is the Democratic front-runner: Mrs Clinton has raised a formidable amount of money, lined up extensive backing and has the country’s top political strategist for a spouse. Mr Obama’s bigger advantage is that the party is actually excited about him and thinks he could win. If Mr Obama decides later this year to enter the presidential race, I expect that he, not Mrs Clinton, will rapidly become the de facto Democratic front-runner. If Mr Obama chooses not to run, he may still sap Mrs Clinton’s strength the way Colin Powell did Bob Dole’s in 1996, by reminding Republican voters that their favourite candidate was not available.