Republicans will be making a mistake if they take Joe Biden's old seat for granted. By Mark Willen, Senior Political Editor July 22, 2010 With House control seemingly within their grasp, Republicans have begun to dream of adding the Senate, but there’s no way to do that without winning Vice President Joe Biden’s old seat in Delaware. The conventional wisdom for months has been that GOP Rep. Mike Castle would walk to a victory over lesser known Democrat Chris Coons. Most of the analysts who track specific races make Castle a heavy favorite, but this race may turn out to be a close one.A Rasmussen poll taken July 10-11 showed Castle with a 47%-36% lead over Coons. That may seem like a comfortable cushion, but it’s not -- not when you consider that Castle led 55%-32% in April. And not when you consider that Castle was under the 50% mark -- generally considered the danger zone for incumbents. Castle isn’t an incumbent per se, but he’s close, having served the entire state in the House for 18 years and before that as governor for eight years. Castle is an icon in Delaware, having never lost an election, but his lead rests in part on the fact that he’s better known than Coons, the New Castle County executive who took up the Democratic mantle after Biden’s son Beau decided against running. Beau Biden was actually running ahead of Castle in early polls, a sign that Castle isn’t a guaranteed winner in the state, which is heavily Democratic. It hasn’t voted for a GOP presidential candidate in more than 20 years. Castle can’t exactly run against Washington in this anti-incumbent year, but Coons can. And though Castle has a well-earned reputation as a moderate who works with Democrats, he has no real congressional accomplishments to his name. Plus he voted against the stimulus, health care and financial regulatory bills -- all of which are relatively popular in Delaware. In fact, it is one of the few states in which the stimulus is regarded as a success, according to the Rasmussen poll. Castle’s age, 71, may also work against him in the race against the 46-year-old Coons. Advertisement Coons certainly has problems of his own. To help balance the budget of New Castle, the state’s largest county, he raised taxes, and that will undoubtedly feature prominently in campaign commercials. But he can counter by pointing to big spending cuts as well. Plus Coons can count on help from big Democratic guns. Biden will work hard to keep his old seat from going to the GOP. And expect Obama, who is still popular in the state, to campaign and raise funds as well. By November, this will be a neck-and-neck battle. Much will depend on the state of the economy and whether Democrats get enthusiastic enough about Coons to show up at the polls. Republicans will be making a big mistake if they continue to take the seat for granted.