More excellent news for Republicans, as South Dakota Senator Tim Johnson is expected to announce today that he will not seek re-election in 2014.

Reuters:

Senator Tim Johnson, the Democratic chairman of the powerful banking committee, does not plan to run for re-election when his current term ends in 2014, two sources familiar with the matter and a Capitol Hill staffer said on Monday.

Johnson, 66, a three-term senator from South Dakota, has scheduled a news conference for Tuesday in his home state to discuss what his aides described as "his future plans."

His retirement would leave a vacant seat in a conservative-leaning state that could be difficult for Democrats to defend as they try to protect their majority in the Senate.

Political analysts expect Johnson's son, Brendan Johnson, who is South Dakota's U.S. attorney, to emerge as a potential Democratic candidate in the 2014 election. The younger Johnson has not announced any formal plans to seek the Senate seat.

Former Democratic Representative Stephanie Herseth Sandlin, who lost a bid for reelection in 2010, is another leading choice to run if the incumbent senator retires, analysts said.

Johnson's exit from Congress would create an opening at the top of the banking committee, which he has led since 2011.

Currently, Rhode Island Senator Jack Reed is the second-ranking Democrat on the panel. However, Reed might take on a leadership role over the Senate Armed Services Committee for retiring Senator Carl Levin, based on his seniority in Congress.

New York's Chuck Schumer is next in line to take over the gavel after that, followed by New Jersey's Bob Menendez, and then Ohio's Sherrod Brown.

Johnson is the 5th Senate Democrat to announce his retirement, following Jay Rockefeller, Tom Harkin, Frank Lautenberg and Carl Levin. The GOP has an excellent chance at pickups in 2 of those races - West Virginia and South Dakota - and will be competitive in Iowa.

On the GOP side, Saxby Chambliss and Mike Johanns have announced their retirement. Neither of those seats is expected to flip.