Multiple GOP sources are saying that Rep. Mike Castle (R-DE) will run for U.S. Senate in Delaware and make his announcement this afternoon.
In addition, Attorney General Beau Biden (D) is expected to soon announce he'll seek the Democratic nomination for his father's old seat.
Politico: "His decision is poised to set up a marquee matchup between two of the biggest names in Delaware politics. The moderate congressman and former Delaware governor has never lost a political race since elected to the Delaware state House in 1966."