Fran Townsend, President Bush's domestic security advisor, announced today that she was resigning, the latest in a series of senior officials to leave the administration as the president juggles a still-full agenda.

Townsend, who began working for the government as an assistant U.S. attorney in Brooklyn, N.Y., rose over two decades and the administrations of four presidents to become a regular fixture in the Oval Office and on Sunday talk shows -- delivering confidential reports to the president and security warnings to the public as the homeland security threat evolved.

She gave no reason for her departure, other than to say she wanted to shift to the private sector. In a handwritten letter she delivered to Bush on Nov. 6, Townsend said she was leaving with "a heavy heart" but had "decided to take a respite from public service."