When the billionaire Warren Buffett wants the rich to be taxed more, the Republicans oppose it at their peril. That, at least, is Barack Obama’s bet. A millionaires’ tax is the big new idea in the president’s latest plan to control the medium-term deficit, which comes on the heels of his call for a new stimulus to revive the US economy.

Republicans call it class warfare. That is hypocritical hyperbole: the accusation fits many Bush-era fiscal decisions better. But they are right that the measure is more of a political trick than a sound policy effort. Little can be said of its economic merits – both because Mr Obama glosses over the detail, and because it borders on insignificance except as part of a comprehensive medium-term fiscal plan.

For any such plan to be sensible, it must combine spending restraint and tax increases, as Mr Obama’s new plan does. It should also overhaul a federal tax system ripe for reform. More rational taxation can raise more revenue from lower rates while increasing predictability and simplicity for private business. This, of course, is what the Bowles-Simpson fiscal responsibility commission proposed last year. Mr Obama could have fought for these principles then. Not having done so, he now faces a steeper uphill battle after the poisoned politics of debt ceiling farce.