Last month, the United States Congress succumbed to Citigroup's lobbying and repealed a key provision of the 2010 Dodd-Frank Wall Street Reform and Consumer Protection Act: the rule that bars banks from trading derivatives.

The Dodd-Frank law's aim was to prevent another financial crisis like that of 2007-2008; the repeal reduces its chances of success.

Derivatives are contracts that derive their value from changes in a market, such as interest rates, foreign-exchange rates, or commodity prices. Banks can use derivatives to hedge risk — say, by ensuring that oil producers to which they lend lock in today's prices for their product through derivatives contracts, thereby protecting themselves and the bank from price volatility.