The intervening time between the Iraq commands was spent at Fort Leavenworth, where Petraeus further developed his military doctrine and pursued an important White House contact in Meghan O'Sullivan who was the principal adviser to the president on the war. In January 2007, as part of his overhauled Iraq strategy, President George W. Bush announced that Petraeus would succeed Gen. George Casey as commanding general of MNF-I to lead all U.S. troops in Iraq. In his memoirs, President Bush likened his selection of Petraeus to the elevations of other great generals of American history, writing, "Lincoln discovered Generals Grant and Sherman. Roosevelt had Eisenhower and Bradley. I found David Petraeus and Ray Odierno.” On January 23, the Senate Armed Services Committee held Petraeus's nomination hearing, during which he testified on his ideas for Iraq, particularly the strategy underpinning the "surge" of forces. During his opening statement, Petraeus stated that "security of the population, especially in Baghdad, and in partnership with the Iraqi Security Forces, will be the focus of the military effort." He went on to state that security will require establishing a persistent presence, especially in Iraq's most threatened neighborhoods. He also noted the critical importance of helping Iraq increase its governmental capacity, develop employment programs, and improve daily life for its citizens.