The Homeland Security Department's second-in-command resigned Monday, citing personal financial reasons.

Michael P. Jackson, the department's deputy secretary, has had a major hand in running the large department, particularly in putting the current management team in place.

In an e-mail to staff Monday, Jackson said, "The simple truth, however, is that after over five years of serving with the president's team, I am compelled to depart for financial reasons that I can no longer ignore."

Jackson makes $168,000 a year. His resignation is effective Oct. 26. In a statement Monday, Homeland Security Secretary Michael Chertoff called Jackson "my most trusted counselor and a close personal friend."

Jackson was deputy secretary of the Transportation Department between 2001 and 2003, during which time he helped set up the Transportation Security Administration. He came to the Homeland Security Department in March of 2005.

From late 2003 to 2005 Jackson worked in the private sector as senior vice president of AECOM Technology Corporation. In his e-mail Monday, Jackson said, "Today I become, in Washington's argot, a lame duck."