The chairman of the Armed Services Committee, California Rep. Buck McKeon, will announce his retirement today, according to sources close to the congressman.

The Hill:

The powerful lawmaker's retirement is likely to spark a battle for his chairmanship - and lead to a competitive race for his House seat.

Democrats are hopeful they could compete for McKeon's slightly Republican-leaning district in Southern California now that he's retiring.

President Obama won 48 percent of the vote there in 2012. Lee Rogers (D), who held McKeon to under 55 percent of the vote in 2012, is running again and had $180,000 in the bank as of the end of September.

McKeon is the latest in a series of senior lawmakers to announce his retirement. A total of 16 congressmen have announced they would not seek reelection at the end of this term.

Rumors have swirled for months that McKeon was likely to retire. His longtime chief of staff, Bob Cochran, left his office in late 2012 and two local Republicans - 2012 congressional candidate and former California state Sen. Tony Strickland, and California state Sen. Steve Knight (R) - had already said they would run if he retires.

McKeon has been chairman of the powerful House Armed Services Committee since 2011 and has been a vocal advocate against cuts to the Pentagon budget stemming from sequestration.

His departure will mark yet another change at the top of the four defense committees in Congress, which all will have chairmen with two years experience or less in 2015.

Both McKeon and Senate Armed Services Committee Chairman Carl Levin (D-Mich.) are retiring at the end of this term. The Appropriations Defense subcommittee chairmen, Sen. Dick Durbin (D-Ill.) and Rep. Rodney Frelinghuysen (R-N.J.), took over the panels after the deaths of Sen. Daniel Inouye (D-Hawaii) and Rep. Bill Young (R-Fla.).

There will likely be a battle for McKeon's chairmanship.

Defense industry officials say that Rep. Mac Thornberry (R-Texas), the vice chairman of the panel, is considered the front-runner to be the next chairman.

Thornberry is also McKeon's preferred pick to take over the committee, according to defense sources.

"Thornberry does all the right things. He does what he needs to for the party; he's well thought of on the committee; and Buck wants him to be his heir apparent," said one defense lobbyist. "There's no reason to pass him over."

The chairmanship of the committee derives its power from the amount of campaign contributions donated to the chairman and his favorites by defense contractors. That, and the ability of the chair to funnel lucrative contracts to favored companies sets up a behind the scenes scramble for McKeon's old job.

Of the 16 retiring members, there are now 10 Republicans who have declined to seek re-election. Many of them are in safe districts, but two or three - including McKeon's district - will probably be competitive. On the Democratic side, at least two retiring members represent districts where a Republican has a real shot of winning.

McKeon was an excellent advocate for maintaining America's defense capabilities in an age of tight budgets. His successor will have his hands full.