Following the terrorist attacks of September 11, 2001, the public was alarmed and demanded urgent action to provide homeland security. A wide array of existing government agencies were responsible for different aspects

A UH-60 Black Hawk helicopter from the Department of Homeland Security's Bureau of Immigration and Customs Enforcement flies past the Statue of Liberty in 2003. MIKE SEGAR/REUTERS/LANDOV

of security; none were structured efficiently to deal with terrorism. In the fall of 2001, letters containing anthrax, a biological weapon, arrived in the mailrooms of a tabloid newspaper, a television network, and Congress, indicating that terrorist threats could come in many forms and could prove challenging to stop.

President George W. Bush created the Office of Homeland Security in October 2001, with former Pennsylvania governor Tom Ridge as its director. In January 2003 it was upgraded to a new cabinet-level department, the Department of Homeland Security, with Ridge as the...