WASHINGTON, March 25 (Reuters) - U.S. 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.
"The immediate question becomes who is next on deck. When you go through seniority and those next in line, you have three lawmakers that are likely to pass on the gavel and it could eventually fall to Sherrod Brown to lead the panel," said Isaac Boltansky, a policy analyst at Compass Point Research & Trading.
He noted Brown is one of the most progressive members of the Senate. "Suddenly, we'll get to 2014 with Brown at the helm and one of the most progressive committees in the Senate."
Johnson joined the Senate in 1997 after a decade representing South Dakota in the U.S. House of Representatives. He has faced physical challenges following a blood vessel bursting in his brain in 2006, which has noticeably slowed his speech. He went through physical and speech therapy, and made a comeback and held onto the Senate seat in 2008.
Democratic Senators Tom Harkin of Iowa, Levin of Michigan, Frank Lautenberg of New Jersey and Jay Rockefeller of West Virginia have already announced plans to retire when their terms end. Republicans Saxby Chambliss of Georgia and Mike Johanns of Nebraska also have said they will not run for re-election.
Overall, 35 of the 100 Senate seats are up for election in 2014, of which 21 are now held by Democrats and 14 are held by Republicans. The Republicans need a net gain of six seats to take control of the chamber.
Johnson, who was facing a tough reelection bid and was widely expected not to run next year, took over the lead gavel on the Senate Banking Committee following the retirement of Connecticut Democrat Christopher Dodd.
He has stood in as one of the chief defenders of the Dodd-Frank Act, the 2010 overhaul of the nation's financial regulatory system that largely passed along party lines.
Johnson has also been responsible for ensuring President Barack Obama's political nominees garner the votes needed for confirmation, including Federal Reserve governors and officials at the Federal Deposit Insurance Corp.
The committee recently pushed through two White House appointments, allowing former federal prosecutor Mary Jo White's nomination to lead the Securities and Exchange Commission to head to the full Senate floor, along with Richard Cordray, to continue on as the head of the Consumer Financial Protection Bureau.
During his tenure as the lead Democrat on the banking panel, Johnson has pressed federal regulators and those in the financial services industry. Johnson called Chief Executive Officer Jamie Dimon to speak before the committee in 2012 to question the JPMorgan Chase CEO on billions of dollars in trading losses.
In his time overseeing the banking committee, Johnson has also helped obtain the reauthorization of the National Flood Insurance Program and the Export-Import bank.
While Johnson has held a number of hearings on the U.S. housing finance system and the government's role in the mortgage market, the leading Democrat has yet to press ahead on crafting legislation that would address the future of Fannie Mae and Freddie Mac.