Beau Biden would have a tough time winning against Mike Castle in this anti-Dem environment, even in Delaware (one of the bluest states out there). Not to talk about inside political shit, but Mike Castle (who is a direct descendant of Ben Franklin), is really popular in Delaware, even though he is a Republican and our only Congressman. Beau is young and does not want to lose a race. He has time to wait Castle out and then run almost unopposed. Castle is 70 and Beau is 40. He can wait for Castle to retire in 8 years and then win handily.
So, in 2010, barring anything dramatic, the Democrats will lose the US Senate tothe Republicans.