DOVER, Del. — Longtime Republican congressman Mike Castle said Wednesday that he will not wage a write-in campaign in the U.S. Senate race in Delaware after his stunning loss in the GOP primary to tea party favorite Christine O'Donnell.
The decision by Castle, a former two-term governor and the longest serving congressman in state history, marks an end to a political career that spanned more than four decades. Since his primary loss, many of Castle's supporters have urged him to run a write-in campaign for the Senate seat long held by Joe Biden before he became vice president.
"I understand why people care so deeply about this election; I listened closely to many viewpoints and carefully considered the option of staying in the race ... While I would have been honored to represent Delaware in the U.S. Senate, I do not believe that seeking office in this manner is in the best interest of all Delawareans," Castle said in a statement late Wednesday.
Castle had until Thursday afternoon to declare his candidacy in writing to the Delaware elections commissioner.
His decision leaves O'Donnell to face Democrat Chris Coons in November.
"Congressman Castle's years of service to Delaware must be honored," said Daniel McElhatton, a spokesman for Coons. "This coming election, the choices are clear, Chris Coons' record of independence, moderation and job creation versus that of Christine O'Donnell's radical ideology that Delaware voters do not appreciate."
The O'Donnell campaign issued a statement thanking Castle for his service.
"Congressman Castle has served Delaware with distinction and honor and we appreciate his dedication and service to our great state," the statement read.
Delaware Republican Party chairman Tom Ross, who vigorously supported Castle in the primary and described O'Donnell as a liar at one point, also thanked him for his long service to the state.
"I'm sure he took many things into account. I'm sure that ultimately he did the right thing, as he always does," Ross said.
"Ultimately, it's better for people to have a clear choice between someone who is going to be a rubber stamp for Obama's agenda and someone who is going to oppose it," he added.
National Republican Senatorial Committee chairman John Cornyn of Texas had said he would not support a write-in campaign by Castle, and that the group was supporting O'Donnell.
Alaska Sen. Lisa Murkowski has risked the ire of some conservatives for launching a write-in campaign following her loss in that state's GOP Senate primary.
O'Donnell herself ran as a write-in candidate in 2006 after finishing last in a three-way GOP Senate primary. O'Donnell received about 11,000 votes, out of more than 250,000 cast.
O'Donnell soundly beat Castle in one of the ugliest primary contests Delaware has ever seen with the help of the California-based Tea Party Express, which bolstered her campaign by pledging $250,000 to run television and radio ads on her behalf.
O'Donnell and her staunchly conservative supporters characterized Castle as a Republican in Name Only, or RINO, a liberal who often votes with Democrats in Congress while masquerading as a GOP conservative.
They also suggested that Castle, 71, was so frail that he might die before finishing his Senate term if elected, that he might switch parties, and that he was cheating on his wife with a man.
While ignoring O'Donnell for much of the campaign, Castle and state Republican Party eventually fired back with attack ads of their own, criticizing O'Donnell, 41, for lying about her education and record, leaving a trail of unpaid bills that included unsettled campaign debts, tax liens and a default on her mortgage, and using campaign finances for personal expenses.
Ross, the state GOP chairman, described O'Donnell as a liar and fraud who couldn't get elected dog catcher, and the GOP filed a complaint with the Federal Election Commission accusing her of illegally colluding with tea party supporters.
Castle has said he does not plan to personally endorse O'Donnell, but that he would not endorse Coons, either.