This year’s Senate race in Delaware has been an afterthought ever since state Attorney General Beau Biden (D) announced in January that he would not run. What would have been a marquee titanic battle between Vice President Joseph Biden’s eldest son and Rep. Mike Castle, the First State’s most prominent Republican, seemed to turn instead into a lopsided contest in Castle’s favor.

But Democrats are pushing back against that conventional wisdom and insist the race will be highly competitive with New Castle County Executive Chris Coons, the new presumptive nominee.

Democratic officials point to Coons’ good early fundraising, his political base and public service record in populous New Castle County, Delaware’s generic Democratic lean — President Barack Obama carried the state with 62 percent in 2008 — and Castle’s lack of strong Democratic opposition in past races as among the reasons the Senate race shouldn’t be written off as a snoozer.

“A lot of people were disappointed when Beau decided not to run for the seat, but I think people are realizing that Chris is a very credible candidate as well,” New Castle County Democratic Party Chairman Erik Schramm said.

Republican officials invariably describe the Delaware race as one of their party’s best opportunities to pick up a Democratic-held Senate seat. They point to significant early advantages Castle wields over Coons in name identification, statewide popularity and fundraising — not to mention that 2010 is shaping up to be a good Republican year.

But the same Republican officials note that Castle is not someone who takes any race for granted. Early polls show Castle leading Coons by double-digit margins, but Castle and GOP officials expect the gap to close — if only because Castle has nowhere to go but down and the lesser-known Coons has nowhere to go but up.

“I expect the Democratic committees to throw a lot of energy and personnel and dollars into this race, so I fully expect it will be a very competitive race before it is all said and done,” Castle said. “I clearly have a substantial lead now, so it almost has to tighten at this point.”

Because this Senate race is being fought in the vice president’s home state, it will be a referendum on the Obama administration more directly and visibly than other races — perhaps with the one exception being the open-seat contest in the president’s home state of Illinois. Coons is running as a strong supporter of the administration’s economic stimulus and health care overhaul, both of which Castle and every other House Republican opposed.

Democrats brandish those two votes as evidence Castle’s voting record has moved to the right and is now out of step with the views of most Delawareans.

“His recent voting record shows that the Congressman either won’t or can’t break from his party and vote independently for what I think are Delaware’s real interests,” Coons said.

Castle pointed to studies of his voting records that show he breaks with his party more frequently than other Republicans. According to a CQ study, Castle in 2009 sided with his party 76 percent of the time on votes that pitted most Democrats against most Republicans — the 17th-lowest score among House Republicans.

Castle was one of eight Republicans who voted last year for a cap-and-trade climate change bill, though he has since expressed concerns that some of the measure’s provisions would harm the economy. Though he opposed the Democratic health care bill, Castle has also said it’s not feasible to repeal it.

“My voting record is still more independent than almost any other Republican in the Congress,” Castle said. “And that’s part of my criticism of the Democratic Senatorial Campaign Committee, the Democratic National Committee and even Chris — if you don’t vote every single time with the Democrats, you are in their mind not worthy of being in office. I just don’t agree with that. I think sometimes Republicans are right and sometimes Democrats are right.”

That sometimes-contrarian voting record has sometimes irked conservative activists such as Christine O’Donnell, a marketing consultant who is running against Castle in the Republican primary. But the Republican establishment in Delaware and Washington, D.C., is solidly behind Castle, in part because they believe that only a Republican in his centrist mold can prevail in a state that has been trending Democratic.

Democrats have also signaled that they will try to portray Castle’s long service in Washington as a liability at a time when voters are angry with Congress. The DSCC on Monday referred to Castle as a “D.C. insider.”

But Castle sees his long experience as a major asset in that he would hit the ground running in the Senate in a way that Coons could not.

“I believe that he would need some time to get his feet on the ground to learn his way around Washington, D.C.,” Castle said. “Part of it’s just getting to know the players, and I know most of the Senators on both sides of the aisle pretty well.”

GOP officials have signaled that they will bring up vulnerabilities they see in Coons’ service as county executive, including layoffs in the most recent budget and a 25 percent property tax increase in the previous budget.

Coons defended his record, saying he balanced budgets and maintained the county’s triple-A bond rating during challenging economic times.

“We delivered a budget on time and with a real minimum of rancor,” Coons said. “That encouraged me in my gut feeling that this is a community of grown-ups — people who expect their elected officials to talk directly to them and are willing to make hard choices.”

Generational politics could play a role in a race between the 70-year-old Congressman and his 46-year-old challenger. It could draw some comparisons to a Delaware Senate race a decade ago, when then-Gov. Tom Carper (D) defeated Sen. Bill Roth (R), a longtime fixture in Delaware politics. Democrats haven’t focused directly on Castle’s age, but they have alluded to it by describing Coons as a candidate with fresh ideas.

Republican officials rejected any comparison between Castle-Coons and Carper-Roth. One local Republican official noted that Castle is about 10 years younger than Roth was in 2000 and that Castle has run statewide every two years as a House Member instead of every six years as a Senator. Several party officials also said that Castle keeps a vigorous campaign schedule.

“I have seen him get so worked up over an unknown candidate and run as hard as he can,” Delaware Republican National Committeewoman Priscilla Rakestraw said. “Believe me when I tell you that there will be no difference in the amount of effort put out versus Chris Coons than there would have been versus Biden.”