The news that Rep. Mike Castle (R-DE) will be running for Vice President Joe Biden's former Senate seat in 2010 not only represents a decent pickup opportunity for Senate Republicans -- it has also created a very good shot for the Democrats to pick up the open House seat.

Castle himself was always secure in the House seat for as long as he wanted it, and he won re-election with 61% of the vote in 2008, at the same time as the Obama-Biden ticket carried the state with 65%.

But in terms of Delaware politics overall, this has become a very Democratic state, having voted Dem for president in every election since 1992, and also for Democratic governors in all the elections since then, as well. Democrats already have a candidate in the race, former Lt. Governor John Carney, who narrowly lost the primary for governor last year.

"I think it's an overwhelmingly Democratic district," said a Democratic source, "and we have a great candidate who has run and won statewide before, has a great profile and people know him. So it definitely makes it a strong pick-up opportunity for us."

A Republican source acknowledged that this will be a tough race, but doesn't at all view it as being lost: "Delaware's presidential numbers from last year are a little bit misleading, because Joe Biden was at the top of the ticket. It only gave John Kerry 53% in 2004." That number would typically put a district in the ranks of swing seats.

The GOP has had five possible candidates: State Rep. Tom Kovach, who is close to Castle; businessman Anthony Wedo; Ferris Wharton, a former prosecutor who narrowly lost to Beau Biden for state Attorney General in 2006; former U.S. Attorney Colm Connolly; and former state Senate Minority Leader Charlie Copeland.

"I don't want to make it seem like once we have a candidate, that candidate will be a frontrunner," the source said. "I think everyone knows it will be an uphill battle to hold the seat. But I feel confident that we can run a credible candidate and run a vigorous campaign to hold it."