For decades, old brownstones in my hometown of Boston were sold off and carved up into individual units. Today, apartment-dwellers are being evicted as these same buildings are being purchased for millions of dollars so the ultra-rich can turn them back into single-family homes.

It is not surprising, then, that the senator Elizabeth Warren of Massachusetts would make inequality and a wealth tax central to her presidential campaign. The economic problem is that whatever your moral views on soaking the rich, history shows wealth taxes do not usually work.

Ms Warren and Bernie Sanders, her rival for the Democratic presidential nomination, each advocate wealth taxes. Ms Warren aims to levy a 2 per cent tax on assets above $50m and up to 6 per cent on billionaires. Mr Sanders wants rates of 1 to 8 per cent on wealth above $32m.