Sen. Kent Conrad’s decision to retire makes the 2012 Senate map a little easier for Republicans aiming to retake the Senate majority, and it shines a spotlight on Democrats who haven’t yet said whether they plan to seek re-election in what could be a tough cycle for the party.

Sen. Joe Lieberman on Wednesday is widely expected to say he has decided against a re-election bid, opening a seat in Connecticut that Democrats are likely to retain. But Conrad’s move changes the 2012 landscape and won’t help the party stave off a likely loss in North Dakota.

Conrad is the lone Democrat in North Dakota’s delegation, and Republican Sen. John Hoeven’s landslide victory following Sen. Byron Dorgan’s retirement last year may have scared away Democrats on the bench from seeking Conrad’s seat next year.

Roll Call Politics has moved the North Dakota race from Leans Democratic to Leans Republican. With Conrad out and no clear Democratic successor in place, a less competitive race would allow the GOP, just four seats shy of the majority, to focus on other pickup opportunities.

The Lieberman announcement is expected to come at a press conference Wednesday afternoon. His staff was publicly tight-lipped about Lieberman’s intentions, except to say, “The decision has been made for a while.”

Lieberman, an Independent who caucuses with the Democrats, would have a difficult path to victory as a Democrat since he was booted in a Democratic primary in 2006 and campaigned for Republicans in 2008. There are at least two likely Democratic candidates, and Connecticut Republicans have their own contenders.

Former Secretary of State Susan Bysiewicz (D) announced her candidacy Tuesday, and Rep. Christopher Murphy (D) said he would make a decision “very soon.”

On the Republican side, Connecticut GOP Chairman Chris Healy told Roll Call that independently wealthy professional wrestling executive Linda McMahon or narrowly defeated gubernatorial candidate Tom Foley could run strong races.

National Republican Senatorial Committee Chairman John Cornyn (Texas) has long said he expected to return his party to the majority over the course of two cycles. Republicans are on the offensive: Democrats have 23 seats to defend because of a strong cycle in 2006, and Republicans have only 10.

An NRSC spokesman called North Dakota “one of the strongest pickup opportunities for Senate Republicans this cycle,” pledging the party would invest any resources necessary to win.

In 2010, Dorgan’s retirement announcement less than three months before the state parties’ conventions left Democrats scrambling to find a nominee. The Democratic Senatorial Campaign Committee did little to help state Sen. Tracy Potter, writing off the seat early to focus on more competitive races.

Conrad’s surprise announcement left state Democrats wondering who might jump in. Some obvious choices are Potter and ex-Rep. Earl Pomeroy, who lost to now-Rep. Rick Berg (R) by 10 points in November. Pomeroy, who now works for Alston & Bird in Washington, D.C., didn’t rule out a bid. Former state Attorney General Heidi Heitkamp and her brother, former state Sen. Joel Heitkamp, have been mentioned. Roger Johnson, now the president of the National Farmers Union, told Roll Call he isn’t interested in the job.

Other potential Democratic contenders mentioned by state sources include state Senate Minority Leader Ryan Taylor, Fargo Deputy Mayor Tim Mahoney, former state Rep. and Dorgan Chief of Staff Pam Gulleson, Conrad State Director Scott Stofferahn, and small-businesswoman Kristin Hedger.

But there’s no shortage of candidates on the Republican side. Public Service Commissioner Brian Kalk announced last week that he has formed an exploratory committee, and most Republicans elected to statewide office have been mentioned for the Senate race, including Berg, Gov. Jack Dalrymple, Lt. Gov. Drew Wrigley, Attorney General Wayne Stenehjem and Tax Commissioner Cory Fong. Fong, busy with the legislative session and tax season, said he won’t make a decision about the Senate race for several months.

“I think that it’s going to be a great opportunity for Republicans to field a very strong candidate,” Fong told Roll Call.

North Dakota is far from the only state where a retirement might dramatically alter a Senate race.

Other Democratic Senators may be thinking about retiring: Sen. Herb Kohl hasn’t announced re-election plans, and since he will turn 76 in February, observers in Wisconsin have questioned whether he will run again.

Sen. Jim Webb also has not given much indication about his plans. The Virginia Democrat could face a rematch with former Sen. George Allen (R), whom Webb defeated in one of the biggest upsets of 2006.

Webb’s decision may come by the end of March, but former Virginia Gov. Tim Kaine said on MSNBC on Tuesday that he fully expects the Senator to run for re-election. Kaine, chairman of the Democratic National Committee, also took himself out of the running for the seat should Webb retire.

In New Mexico, Sen. Jeff Bingaman is taking his time to decide whether to run for a sixth term, which has led to speculation he may retire. The Democrat has some fundraising, but while he contemplates the future, former Rep. Heather Wilson (R) has told Roll Call she is considering running.

Sen. Daniel Akaka (D), 86, has insisted he’ll seek a fourth term, announcing in Hawaii he’s ready to run.

Early activity doesn’t make re-election bids a certainty. After all, Conrad had already run radio ads back home this month defending his record, even though sources told Roll Call he decided over the holidays not to run.

Though Democratic retirements will have the biggest impact on the Senate playing field, the first Senator to announce she won’t run for re-election was Sen. Kay Bailey Hutchison (R-Texas). Three Republicans have already kicked off Senate campaigns: former Secretary of State Roger Williams and Railroad Commissioners Michael Williams and Elizabeth Ames Jones. Others, such as Lt. Gov. David Dewhurst and Dallas Mayor Tom Leppert, are reportedly looking at the race.

The top Republican on retirement watch is Sen. John Ensign. The second-term lawmaker has said he intends to run for re-election, but insiders and experts in Nevada believe that given his ethics troubles he would have a difficult time in a GOP primary against Rep. Dean Heller, who is considering making the jump.

Ensign told reporters in Nevada last week that he knows his race would be “very, very difficult” and said he plans voter outreach “to try to earn their trust back.”

Steve Peoples and Kyle Trygstad contributed to this report.