With 51 votes in the Senate, Democrats fall far short of the numbers they need to break a filibuster (60) or override a veto (67), so their legislative record this session is likely to be meager. But they are already making their mark in another way – oversight.

As the majority party in both houses, Democrats control committee agendas, hearing schedules and witness lists. Perhaps their most important power can be summed up in one word: Subpoena.

An excellent example of this power occurred last week when the Senate Subcommittee on Investigations, headed by Carl Levin of Michigan, summoned three executives of credit card companies to explain some of their more outrageous and abusive practices. Even before the hearing, two of the companies announced changes in those practices and issued apologies to their customers.

Citigroup ended “universal default,” which allows companies to raise credit card interest rates when a customer is late in paying any bill, say from an electric utility or cable provider. Citi also dropped their practice of arbitrarily raising rates at any time for any reason. Now, charges can rise only when a card expires or a customer defaults.