Former Delaware Lt. Gov. John Carney (D), filed Wednesday morning to challenge longtime Rep. Mike Castle (R-Del.) in 2010.

In his announcement, Carney stressed his ability to transcend partisanship — a theme that will no doubt be echoed during the campaign against a well-known and respected moderate like Castle.

“I’ll be that kind of leader in Congress — one who works with both Republicans and Democrats to move our country forward, starting with a focus on creating jobs and getting our economy back on track,— he said.

Carney’s move sets up what is expected to be a competitive race for Castle, a well-known moderate and popular former governor who has always cruised to re-election in the state’s at-large seat.

But Carney would also be well-positioned in an open-seat race if Castle decides to retire or forgo another term in the House and run for Senate.

Sen. Ted Kaufman (D-Del.), who was appointed to the seat formerly held by Vice President Joseph Biden, has said he will not run for the remainder of Biden’s Senate term in 2010, setting up an open-seat race. Delaware Attorney General Beau Biden (D), the vice president’s son, is viewed as likely to run for his father’s old Senate seat.

According to recently released Federal Election Commission reports, Castle had about $840,000 in the bank as of March 31 but had raised a little less than $75,000 in the first three months of the year.

In his announcement Wednesday morning, Carney invoked the vice president and the state’s other Democratic Senator, Tom Carper.

“In the tradition of vice president and former Sen. Biden and Sen. Carper, I’ll be a strong, independent voice in Congress for all Delawareans and I will work with President Obama and his administration to get our economy moving again and to address the significant challenges we face as a country,— he said.