The 2010 U.S. Senate race in Delaware is all about the candidates who haven’t decided whether to run yet.

The first Rasmussen Reports Election 2010 survey in the state finds that longtime Republican Congressman Mike Castle beats state Attorney General Beau Biden by five points – 47% to 42% - in a hypothetical match-up for the seat Biden’s father held for 36 years. Five percent (5%) like some other candidate, and six percent (6%) are undecided.

Against the only declared GOP candidate for the race, Christine O’Donnell, Biden wins by nine points – 49% to 40%. Three percent (3%) prefer another candidate, and eight percent are not sure (8%) how they’ll vote.

Castle carries the male vote by 25 points, while Biden fares better among women by 13 points. While both candidates get over 70% support from those in their respective parties, Castle wins voters not affiliated with either party by a two-to-one margin.

O’Donnell wins men by 10 points but loses women by 27. She gets 71% Republican support, while Biden picks up 83% of Democrats. But O’Donnell also has nearly a two-to-one edge among unaffiliateds.

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Joe Biden defeated GOP candidate O’Donnell, a political commentator and marketing consultant, last November with 65% of the vote. Delaware law allowed him to run for reelection and the vice presidency at the same time.

When Biden resigned the seat to become vice president, the governor appointed Ted Kaufman, a longtime Biden aide, to take his place for two years. Kaufman has said he will not run for a full term in the 2010 special election to fill the remaining four years of Biden’s term.

Beau Biden, who just completed a year-long Army National Guard deployment in Iraq, has still not said whether he intends to enter the Senate race. He is considered the leading Democratic contender for the job.

According to the Associated Press, Castle, a former governor and the longest-serving congressman in Delaware history, has never lost a race since being elected to the state House in 1966. He is viewed as the leading GOP candidate for the Senate race but so far has not said whether he is running.

Twenty-five percent (25%) of Delaware voters have a very favorable view of Castle, while 15% regard him very unfavorably. Just five percent (5%) have no opinion of him.

Biden is viewed very favorably by 26% and very unfavorably by 12%. Nine percent (9%) aren’t sure what they think of him.

For O’Donnell, very favorables total 14%, with very unfavorables at 15%. She has a bit more of a name-recognition problem since 19% don’t know her well enough to even venture a soft opinion.

At this point in a campaign, Rasmussen Reports considers the number of people with a strong opinion more significant than the total favorable/unfavorable numbers.

Delaware voters have a little more favorable view of the health care plan proposed by President Obama and congressional Democrats than do voters nationally. Forty-eight percent (48%) in Delaware favor the plan, while 49% oppose it. Thirty-three percent (33%) strongly favor, 39% strongly oppose.

Forty-three percent (43%) say the quality of health care will get worse if the plan becomes law, but 32% say it will get better. Sixteen percent (16%) expect it to stay the same.

Fifty percent (50%) say the cost of health care will go up if the plan passes, while 26% say costs will go down as the president and other supporters contend. Again, 16% think there will be no change.

Sixty-two percent (62%) say passage of the health care plan will increase the federal budget deficit, and 72% say it is at least somewhat likely that taxes on the middle class will be increased to cover the cost of the plan. Fifty-five percent (55%) say a middle-class tax increase is very likely.

Eight percent (8%) of Delaware voters rate the U.S. economy as good or excellent, while 44% say it is poor. Thirty-one percent (31%) say the economy is getting better; 42% say it’s getting worse.

But like the rest of the country, a majority (52%) of voters in Delaware worry that the federal government will do too much in reacting to the country’s economic problems. Thirty-three percent (33%) fear the government won’t do enough.

Barack Obama carried Delaware with 62% of the vote last November, and 54% of voters in the state approve of the job he is doing as president. Forty-five percent (45%) disapprove of the president’s performance. Thirty-five percent (35%) strongly approve, while the identical number (35%) strongly disapprove. This is better than Obama’s job approval ratings nationally as measured by the Rasmussen Reports daily Presidential Tracking Poll.

Fifty-nine percent (59%) approve of Jack Markell’s performance as governor, including 12% who strongly approve. Thirty-seven percent (37%) disapprove of the job the Democrat is doing, with 12% who strongly disapprove.

Rasmussen Reports has begun surveying potential 2010 Senate match-ups and has released findings from Arkansas, California, Colorado, Connecticut, Iowa, Missouri, Nevada, New Hampshire, New York, North Carolina and Ohio.

We also have released recent data on the 2009 governor’s race in New Jersey and Virginia along with the 2010 governor’s races in Arizona, California, Colorado, Iowa, New York and Ohio.

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