(CNN) - A new poll suggests that Delaware Republicans might have blown their chance to win back a Senate seat long held the by the Democrats.
According to a CNN/Time/Opinion Research Corporation poll released Wednesday, 55 percent of likely voters in Delaware say that they are backing Democratic Senate nominee Chris Coons, with 39 percent saying they support GOP nominee Christine O'Donnell. Among the wider pool of registered voters, Coons' leads O'Donnell by 25 points.
Last week O'Donnell upset longtime moderate Republican Rep. and former Gov. Mike Castle in the state's primary. O'Donnell, a conservative commentator who launched unsuccessful Senate bids in 2006 and 2008, was supported and helped by Tea Party activists and by former Alaska Gov. Sarah Palin.
But the survey indicates that if Castle had won the primary, he would be leading Coon's 55 to 37 percent in the general election matchup.
"Castle would have had a significant ideological and geographical advantage over O'Donnell," says CNN Polling Director Keating Holland. "Castle would have had a 24-point lead among independents, but O'Donnell appears to have a seven-point deficit among them. Castle would have also had a 19-point edge in New Castle County, the most populous part of the state, but O'Donnell is losing that key region by 18 points."
According to the survey, a small but significant chunk of Republican voters may be helping to put Coons over the top. "CNN has conducted polls in nine other Senate races this fall, and the Democratic candidate has never gotten double-digit support among Republicans in any of them. But 15 percent of Delaware Republicans are choosing Coons. That may not sound like much, but in today's polarized political environment, it's a big advantage that any Democrat would like to have," Holland said.
The poll also indicates that Coons, the executive of New Castle County, holds a nearly two to one advantage among female voters, and takes 49 percent of the male vote to O'Donnell's 46 percent. Coons also has a 15 point advantage over O'Donnell among voters 50 and older, who tend to make up a larger percentage of the electorate in midterm elections than they do during presidential election years.
The winner in November will fill out the remaining four years of Vice President Joe Biden's final term in the Senate. Biden, who served in the Senate for nearly four decades, stepped down from his seat after his election in November 2008 as vice president. Former Biden aide Ted Kaufman was named as an interim replacement, and is not seeking a full term. After much speculation that he would run for his father's old seat, Delaware Attorney General Beau Biden announced in late January that he would instead run for re-election as Delaware attorney general. Coon's announced days later and faced no serious opposition for the Democratic party's nomination.
The CNN/Time/Opinion Research Corporation poll was conducted September 17-21, with 1,366 registered voters in Delaware, including 703 likely voters questioned by telephone. The survey's sampling error is plus or minus 2.5 percentage points for registered voters and 3.5 percentage points for likely voters.
- CNN's Deputy Political Director Paul Steinhauser contributed to this report