Rep. Mike Castle is planning on polling a potential three-way Senate race to test his chances as a write-in candidate, a Delaware Republican tells POLITICO. Castle, who lost his GOP primary by a 6-point margin to tea party upstart Christine O’Donnell nine days ago, opened the door to a potential write-in bid Wednesday evening when he told reporters off the House floor it was still a possibility he was considering. The GOP source did not have specifics on when Castle’s team would conduct the poll, but viewed it as a practical step even if the nine-term congressman was unlikely to re-enter the race. A spokeswoman for Castle, who put the chances of him running as a write-in “under 5 percent,” said her boss likely wouldn’t settle on a final decision before next week. According to the state Elections Commission, Castle would have to complete a form by next Thursday to officially qualify as a write-in candidate. Said Castle spokeswoman Kate Dickens: “A lot of encouragement has come in, nice calls from people in Delaware who want an independent voice.” Dickens, who would not confirm a plan to poll, said Castle has mostly been focused on House business, but has taken calls from those urging him to pursue a bid without a party banner. Delaware GOP National Committeewoman Priscilla Rakestraw said she has fielded dozens of calls over the last 48 hours, mostly from Democrats, about a potential Castle write-in campaign. “They want to organize a write-in campaign. I’m stunned. Obviously, they don’t like their option of voting for Chris Coons. I pass them along to Mike Castle’s organization. I think they are waiting for a nod from Castle,” Rakestraw said. Rakestraw said that a Castle bid would likely test her loyalties. “Everyone knows of my relationship and loyalty to Mike Castle. I make no secret of that. I might have to make a tough decision.” While Delaware Republicans still believe the chances of Castle making the leap is unlikely, top GOP leaders in Washington sent a strong message Thursday that they would stay united behind O’Donnell. "The Senate campaign committee's view is once the nominee is determined, that's who we support,” said Arizona Sen. John Kyl, the minority whip. A CNN/Time poll showed released Thursday showed Democratic nominee Chris Coons as a heavy favorite against O’Donnell, holding a 16-point lead.http://www.politico.com/news/stories/0910/42649.html