EXITING STAGE RIGHT…. With a caucus down to just 41 members, Senate Republicans need to keep retirements to a minimum in order to conserve campaign resources and maximize likely victories.

And yet, a surprising number are already exiting stage right.

Sen. Kit Bond, the senior Republican from Missouri who sits on powerful Senate committees, announced Thursday that he will not run for reelection in 2010, giving Democrats a shot to pick up a seat in a state that has emerged as a major battleground. […]

Missouri has emerged as a battleground state, after Claire McCaskill (D) defeated incumbent Republican Sen. Jim Talent in 2006 and Barack Obama lost the state by less than 5,000 votes to John McCain in the 2008 elections. And Missouri voters just elected Jay Nixon, a Democrat, as their next governor, signaling that Bond could face a tough challenge if he ran for a fifth term.

Perhaps most notably, Bond is the third incumbent to announce their retirement in advance of the 2010 cycle, following Mel Martinez (Florida) and Sam Brownback (Kansas), while Kay Bailey Hutchison (Texas) is planning a gubernatorial campaign that will create a fourth Republican open-seat contest. At least three of these four were likely shoo-ins for re-election.

What’s more, with four more Republican incumbents likely to face major challenges next year — Burr in North Carolina, Gregg in New Hampshire, Specter in Pennsylvania, and Voinovich in Ohio — Bond’s announcement makes the 2010 cycle that much more difficult for the GOP.

As for Missouri, Secretary of State Robin Carnahan and state Attorney General Chris Koster are two major Democratic candidates to keep an eye on, while among Republicans, Rep. Roy Blunt is reportedly eyeing the race, as is former Sen. Jim Talent, who lost his Senate seat in 2006 to Claire McCaskill.

Our ideas can save democracy... But we need your help! Donate Now!

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.