"The president behaved like a virtual criminal but we didn't have the courage to sack him for fear of violating the American constitution," Vidal told the El Mundo newspaper.
The author, a trenchant critic of the US-led invasion of Iraq, said it would take the United States "100 years to repair the damage" caused by Bush.
"We live in a dictatorship. We have a fascist government ...which controls the media," he said.
Vidal also said presidential aspirant Barack Obama was "intelligent" adding that it would be a "novelty" to have an "intelligent" person in the White House.