Betty Castor, Florida's former education commissioner, has been accused of not being tough enough on a professor when she was president of the University of South Florida, The Miami Herald reported Wednesday.
Professor Sami al-Arian has since been arrested and is awaiting trial on charges he helped finance Palestinian terrorists.
Castor's opponents say she should have fired him. Castor said she did not have enough evidence at the time to do that.
Graham said she did the best she could considering the circumstances.
Earlier this month, Graham came to the defense of another candidate, Miami-Dade County Mayor Alex Penelas who Rep. Peter Deutsch, another candidate, said bailed out on former Vice President Al Gore's campaign in 2000.
"Senator Graham has described his role as guardian of the facts during the primary," said Paul Anderson, Graham's spokesman.
The primary will be held Aug. 31.