A Rep. Mike Castle (R-Del.) campaign source confirmed to The Hill late Tuesday that the longtime congressman will not be endorsing Christine O'Donnell.
The Tea Party-backed O'Donnell defeated Castle for Delaware's Republican Senate nomination.
After the stunning primary loss, Castle's campaign also said the longtime
congressman is not interested in waging a write in bid this November.
In Alaska, Sen Lisa Murkowski (R-Alaska) is contemplating an independent write in campaign after she lost to Tea Party backed Joe Miller in the August GOP primary.
As to whether the national party would back O'Donnell, a Castle campaign source said the campaign has no knowledge of their thinking but said "they should save their money."