Tom Ridge, the nation's first homeland security secretary, announced Tuesday that he was resigning after three years of reworking U.S. security and presiding over color-coded terror alerts. Ridge, the seventh officer to leave Bush's Cabinet so far, oversaw the most significant government reorganization in 50 years. Ridge said he would remain on the job through Feb. 1, unless his replacement was installed sooner. President George W. Bush said in a prepared statement Tuesday evening: "His efforts have resulted in safer skies, increased border and port security and enhanced measures to safeguard our critical infrastructure and the American public." Ridge sent his letter of resignation to Bush at midday Tuesday after attending a morning White House threat briefing with CIA and FBI officials. Ridge thanked Bush for giving him the opportunity to fight back against terrorists, as did the passengers on Flight 93, who forced their hijacked plane down in a Pennsylvania field. "There will always be more to do, but today, America is significantly stronger and safer than ever before," Ridge wrote Bush.