Updated: 11:18 a.m.

The ripple effect from the upcoming retirement of Sen. Joe Lieberman (I-Conn.) will take months to shake out, but Republicans are quietly confident that the moving pieces will create at least one opportunity to expand their House majority in 2012.

The GOP is already eyeing Connecticut’s 5th district seat, whose current occupant, three-term Rep. Christopher Murphy (D), announced Thursday that he would run to replace Lieberman.

“This is a competitive district to begin with,” said National Republican Congressional Committee spokesman Tory Mazzola. “But as an open seat, Democrats’ troubles of trying to hold it are that much more magnified.”

Conventional wisdom suggests that Republicans will play far more defense than offense in 2012 as they fight to maintain their historic gains of the 2010 midterms. The GOP sees Murphy’s seat as one of a handful of Northeastern pickup opportunities in the next cycle.

Other 2012 targets include Pennsylvania’s 4th district, where Rep. Jason Altmire (D) eked out a 2-point victory in November; New York’s 23rd district, where Rep. Bill Owens (D) has twice benefited from a split Republican vote; and New York’s 1st district, where Rep. Tim Bishop (D) had to wait a month before his 300-vote lead persuaded his Republican challenger to concede.

“I think it’s reasonable to think Republicans will be on offense in 2012,” said one GOP operative, who acknowledged the party’s need to focus on defense as well.

Republicans will have to fight to win a seat in Connecticut, however.

The Nutmeg State is one of the last Democratic strongholds in the nation: Democrats swept every statewide office, a Senate seat and all five House districts in November. But Mazzola notes that the 5th district is the most competitive.

A Republican, Rep. Nancy Johnson, held the seat as recently as 2006. Sen. John Kerry (D-Mass.) essentially tied President George W. Bush in the district in the 2004 presidential election, winning by roughly 1,000 votes. Four years later, Barack Obama earned 56 percent of the vote against GOP presidential nominee John McCain, in what was Obama’s weakest performance in any of Connecticut’s Congressional districts.

The NRCC is already encouraging 2010 candidate Sam Caligiuri, a lawyer and former state Senator, to run again. He lost by more than 8 points but forced Murphy to spend millions in the process.

“Sam is giving serious consideration to running again. I think he will,” said Evan Kozlow, Caligiuri’s consultant during the 2010 cycle who maintains “very tight” contact with the candidate. “There’s a lot happening in Connecticut with the Lieberman announcement. We’ll wait and see what Murphy does. Certainly, I think an open seat is a little more enticing.”

Kozlow said Caligiuri has cause for future optimism: He was weakened by a costly and divisive GOP primary in 2010, a process that Kozlow hoped would not be repeated in the next cycle. Murphy spent $3 million to Caligiuri’s $1.5 million on the race, a figure that a less well-known Democrat might struggle to raise. And Caligiuri made significant strides in building name identification, “which puts him in a much better place,” Kozlow said.

The Democratic field has been reluctant to take shape before Murphy takes his next step, but Democrats to watch include state Speaker Chris Donovan and Simsbury First Selectwoman Mary Glassman.

The 5th district might not be the only trouble spot for Connecticut Democrats in 2012.

Rep. Joe Courtney (D) of the 2nd district is also mulling a run for Lieberman’s seat. “Over the past few months, people from across Connecticut whose advice I respect have encouraged me to consider a Senate run. I am seriously considering that challenge,” Courtney said in a statement earlier in the week.

The 2nd district, the state’s largest geographically, is slightly more favorable for Democrats than the 5th. But local Democrats note that Courtney needed a recount to beat Rob Simmons (R) in 2006.

Democrats say they’re taking nothing for granted. But they are quietly and cautiously optimistic that 2012 will be as good to Connecticut Democrats as 2010.

Murphy announced his Senate bid Thursday morning.