"Former US Secretary of State Colin Powell has said he fails to understand why better preparations were not made before Hurricane Katrina struck."
There were "a lot of failures at a lot of levels - local, state and federal", Mr Powell told ABC.
"There was more than enough warning over time about the dangers to New Orleans - not enough was done," he said.
Mr Powell's views will be heard with particular interest as he is a highly respected figure and a prominent black American, the BBC's Justin Webb reports from Washington.
The Pew Research Center, which ran the new opinion poll, also indicated that two-thirds of the African-Americans questioned believed the government reaction would have been faster if most of those affected had been white.
But Mr Powell said so many African-Americans were left unprotected because they were poor, rather than because they were black.
It "should have been a blinding flash of the obvious... that when you order a mandatory evacuation, you can't expect everybody to evacuate on their own", he said.
Who are these 28% who think that Bush did all that he could?! Even if you don't hold Bush accountable, who in their right mind would say he did every last thing he possibly could?!