When President Obama, the supreme rationalist, says that there are just days to avert Armageddon, everyone should sit up and listen. For months, Republicans have used their new majority in the House of Representatives to block any move to lift the artificial cap on the amount the US government can borrow. If by this Friday they still refuse – insisting on up to $4trillion of spending cuts, excluding defence, and no tax increases as the price of their support – then the US will be unable to service its public debts. The biggest economy on Earth will default.

The results will be catastrophic, argues JP Morgan chief executive Jamie Dimon – a warning repeated by Obama. The US government will have to start to wind down: soldiers' wages and public pensions alike will be suspended. But in the financial markets there will be mayhem. Interest rates will shoot up and there will be a flight from the dollar. Banks, uncertain about their expected income from their holdings of US Treasury bonds and bills, will call in their loans, creating a second credit crunch. Some may collapse. Even to get days away from such a prospect, says Obama, will now have costs: every creditor to the US has been shaken to the core by American politicians not taking their responsibilities as borrowers seriously. They will exact a higher price for lending in future, even if a bargain is struck now.

But the Democrats cannot agree to the Republicans' absolutist demands, in part because the arithmetic of deficit reduction does not work without tax increases and cuts in defence spending, in part because they passionately believe that with taxes the lowest for 50 years, the US's rich should share in the pain and in part because in any human exchange there is an element of horse-trading. The Republicans want to suspend the rules by which not just Washington but any political system operates. They want to be political winners who take all, risking even the collapse of the US economy to get their way. (...)

There has always been this fundamentalist strand in US life, but what has inflamed it over the last decade is a twofold process – a wrong-headed understanding of why US economic pre-eminence is being challenged, closely linked to the breakdown of a public realm in which ideas are discussed, traded and exchanged in a climate which respects argument. The abolition of the Fairness Doctrine in 1987, which required all broadcasters fairly to represent all points of view, has created a mass media shouting, ranting, sloganising and overwhelmingly from the political right.

The leader in the charge is Rupert Murdoch's Fox News, a TV channel with an audience of 100 million in which all news and comment have to be shoehorned – subtly in its news operation and overtly in its commentary – into a conservative worldview. It operates, as the former White House communications director Anita Dunn has said, "as either the research or communications arm of the Republican party". Leading Republican stars such as Mike Huckabee or Sarah Palin are on its payroll. Its political shows pull no punches: the hosts are hard-line Republicans. If Fox News were to permit the case for tax increases to be fairly reported or discussed it would not be doing its job. Murdoch, refusing in a Fox News interview last week even to discuss the News of the World, would be displeased.