Rep. Michael N. Castle, who has held elective office in Delaware since the mid-1980s, finds himself unexpectedly behind "tea party" favorite Christine O'Donnell in the Republican primary for the Senate. (AP Photo)

Rep. Michael N. Castle, who has held elective office in Delaware since the mid-1980s, finds himself unexpectedly behind "tea party" favorite Christine O'Donnell in the Republican primary for the Senate. (AP Photo)