I didn't assert Bush was harming the nation ---- I do not think the Constitution calls for the role of the President to be that of official State Muezzin.
Certainly plenty of American Presidents have called for national days of thanksgiving, prayer, etc. Other presidents have not. Jefferson resisted such acts, not because he didn't pray, but because he was President - not pope or preacher.
You're correct, that is not among the delineated responsibilities of the President. However, maybe he's asking this of other Americans as a human being who is saddened and concerned for his other fellow human beings in NOLA.
You'd like to pretend that he's signed an Executive Order requiring all Americans to pray or else.
What does that have to do with President Bush asking his fellow citizens to pray on behalf of the victims of Hurricane Katrina?