Despite the current media frenzy, Katrina is likely to be a footnote in the history of the Bush presidency. The real question for Bush's role in history remains Iraq.
Ironically, the short term effect of Katrina was to drive stories about Iraq off the television screens and the front pages of the newspapers. In the short run that helped Bush politically since the news from Iraq just before the storm had not been good. Bush had pleaded with Iraqi politicians to adjust the new draft constitution to attract the disgruntled Sunni Arab minority, but the majority Shia and their Kurdish allies rejected the president's appeal. Since the insurgency is centered among the Sunnis, this refusal is likely to make it more difficult to establish the security that is necessary for democratic government to work.
Because they represent a minority, the Sunni insurgents have little prospect of "winning" control of Iraq the way North Vietnam was able to win control of South Vietnam, but they may be able to disrupt the progress toward a stable constitutional government that Bush needs to be able to claim success for his Iraq policy. At worst, they may be able to foment a civil war among the three parts of Iraq.
Despite claims by the extreme left and right around the world, America is not an imperial nation. American public opinion will support the use of force if people feel threatened or a cause is just, but Americans have little interest in ruling over other people. Neo-conservative appeals to the example of the British empire are far fetched. The idea that American troops will stay in Iraq indefinitely, or "just as long as necessary and not one day more" in the clichéd language of Secretary of Defense Donald Rumsfeld is highly implausible. That means Bush has only a relatively short time to achieve his goals in Iraq. If he is able to produce a stable constitution, a political compromise among the contesting parties, and successful elections, he may be able to declare victory. Right now, the prospects look highly uncertain. Even before the floodwaters of Katrina recede, Bush will need to focus on his Iraq conundrum for that is how his presidency will be judged by history long after Katrina has been forgotten.