The trial ended Thursday with Edwards, D-N.C., acquitted on one count and jurors unable to reach a verdict on other counts involving alleged misuse of campaign funds to support his former mistress.
U.S. Attorney George Holding, appointed by President George W. Bush, began the investigation. Three Justice Department officials, who did not want their names used, said there was little enthusiasm at first for the case after President Barack Obama was elected.
"It would be seen as a bad thing if we protected John Edwards and interfered in the North Carolina investigation by a Republican U.S. attorney," one said was the justification for not dropping the investigation.
The Justice Department has not said whether it will seek a new trial.
Jurors who appeared on national television shows Friday said one of the prosecution's biggest problems was the credibility of its star witness, Andrew Young, a former Edwards aide.