He conceded it would have been a long-shot.
And he ultimately decided against it.
Rep. Mike Castle (R-DE) announced late Wednesday night that he would not launch a write-in bid for Senate. Two weeks ago, Christine O'Donnell shocked the political establishment when she upset Castle in his effort to be the Republican standard bearer for Senate this fall.
After the loss, Castle said he "probably" wouldn't do it. He noted that he wasn't "exactly approaching this with bated breath."
But Castle said that many friends encouraged him to pursue a write-in bid.
The Delaware Republican officially put his Senate aspirations to rest Wednesday.
"I do not believe that seeking office in this manner is in the best interest of all Delawareans. Therefore, it's time for Jane and me to begin thinking about the next chapter of our lives,"Castle said.
Castle needed to file paperwork to be a write-in candidate by the end of the day Thursday.