Mary Schapiro's nomination to lead the US Securities and Exchange Commission comes at one of the most trying periods of its 75-year history.

Once considered a gem of the regulatory world, the agency's relevance - and very existence - have been thrown into doubt after a landslide of criticism for scrutiny failures during the financial crisis. The latest involved missing the $50bn (€37bn, £33bn) "Ponzi" scheme allegedly perpetrated by Bernard Madoff, in spite of credible information apparently brought to its attention many times.