The Delaware attorney general told supporters in an e-mail that he will run for re-election to his state post instead of running against GOP Rep. Mike Castle for the seat the elder Biden held for 36 years. He cited a need to focus on prosecution of high-profile child molestation case.
"I have a duty to fulfill as attorney general, and the immediate need to focus on a case of great consequence. And that is what I must do," Biden, 40, wrote. "Therefore I cannot and will not run for the United States Senate in 2010."
He left open the door of a candidacy in future years.