GEORGETOWN, Del. — The only thing harder than shocking the political world with a come-from-nowhere victory is doing it again seven weeks later.

Even many Republican loyalists think Christine O'Donnell, the tea party darling who capped a summer of primary upsets by wrestling a U.S. Senate nomination from a GOP icon in Delaware, faces a steeper climb on Nov. 2 than she did on Sept. 14.

The man she beat then, nine-term congressman and former governor Michael Castle, was mulling a possible write-in candidacy Friday, a move that could pull some moderate Republicans' votes from O'Donnell, and possibly some independent votes from her Democratic opponent, Chris Coons. The head of the Republican Senatorial Campaign Committee urged Castle not to run.

Coons, 47, is a low-key county executive of Delaware's biggest county, and a man many had expected to lose to Castle in November. O'Donnell's primary victory scrambled that picture, giving Democrats strong hopes of keeping the Senate seat once held by Vice President Joe Biden. A recent CNN-Time poll showed Coons leading O'Donnell by 16 percentage points.