MITT Romney’s campaign claims to be outraged that President Barack Obama would dare criticise its candidate’s experience of running Bain Capital, a private- equity firm. Some Democratic politicians have also said the president went too far in tarring an important driver of economic growth. The financial price has been high: Romney’s campaign is reaping unusually generous Wall Street contributions, while Obama’s campaign is raising far less from the financial sector than it did four years ago.

The Obama campaign, however, is right to make an issue of Romney’s tenure at Bain. Romney argues that his experience in the private sector makes him the best choice to revive the economy, and voters need to understand the precise nature of that experience.

Two weeks ago, the Obama campaign released an ad showing a few of the 750 Kansas City steelworkers who were laid off after Bain Capital bought their company and later sent it into bankruptcy proceedings. “We view Mitt Romney as a job destroyer,” one of them said. The president explained later that Romney’s principal goals in the private equity field are not what the presidency is about.

At Bain Capital, Romney made businesses more efficient, but often at a high human cost. His embrace of Republican budgets that would benefit the wealthy while hurting the poor and the middle class.

Private equity, rarely by design, has created many jobs. But the practice of leveraged buyouts, in which Bain was a big player, has also contributed significantly to the growth of the income gap, moving wealth from the middle class to the top end. The president is helping to remind voters of the direct line between Romney’s previous priorities and the ones he intends to pursue in office.