AMERICA sidestepped one fiscal disaster at the turn of the year when Barack Obama and Congress agreed to keep most tax rates from rising. A much bigger one is as little as five weeks away, when the Treasury Department runs out of legal authority to borrow. Failure to raise the “debt ceiling”, Mr Obama has warned, would force the government to default on its obligations. Republicans say they need some sort of leverage to drag a spendthrift president to the negotiating table. They have a point, but the debt ceiling is a dangerous tool with which to make it.