Securities and Exchange Commission Chairman Mary Schapiro testifies before the Senate Banking, Housing and Urban Affairs Committee about derivatives reform in the Dirksen Senate Office Building on Capitol Hill May 22, 2012 in Washington, D.C. - 

Today, Mary Schapiro, the chairman of the Securities and Exchange Commission, announced she’s moving on. 

The SEC was created in the 1930s, with a mission “to protect investors, maintain fair, orderly, and efficient markets, and facilitate capital formation.” 

It isn’t a big agency. The SEC’s annual budget is just about $1.5 billion -- that’s not much more than what the U.S. Fish and Wildlife Service gets. But the SEC has a lot to do. 

“Everything dealing with Wall Street, in some way, shape, or form, comes and rests at the SEC’s feet,” says Jeffrey Manns, who teaches securities law at The George Washington University.

And Wall Street is a different place today than it was when Congress created the agency after the Great Depression. 

“The markets have grown and changed,” says Hillary Sale, the Walter D. Coles Professor of Law at Washington University in St. Louis. “The complexity is dramatic, and it is very hard to keep pace with that.”

Especially when Congress controls the SEC’s budget.

In 1941, the federal government needed office space. It decided the SEC was a “nonessential agency,” and moved it to Philadelphia.

“Obviously, the war effort -- beating the Nazis and the Japanese -- was a much higher priority than policing the New York Stock Exchange,” says Adam Pritchard, the Frances and George Skestos Professor of Law at the University of Michigan. 

The SEC moved back to Washington in 1947. 

Jeffrey Manns says the agency’s mandate grew again after the most recent financial crisis. It was charged with writing and enforcing dozens of new rules. 

But all that is running behind schedule.

“I think there is certainly a case the SEC lacks the resources it needs to handle the vast scope of its responsibilities,” says Manns.

Critics say the agency hasn’t been proactive enough, that it has had trouble anticipating problems. Still, its supporters argue one important thing hasn’t changed since 1934: U.S. financial markets need some kind of watchdog.

Follow David Gura at @davidgura