Thursday's assault against insurgent strongholds near Samarra by US and Iraqi troops came as the Bush administration issued a new report reaffirming its policy of pre-emptive strikes and directing attention to the dangers of a nuclear-armed Iran. White House officials were quick to deny any connection between the assault, which the military billed as the biggest air operation since the March 2003 invasion, and the national security update. Both came as the administration scrambled to turn around public opinion. Polls show eroding support for the war and slippage in the traditional GOP advantage on national security. President George W. Bush has embarked on a series of speeches defending his Iraq policy.