That didn’t take long.

Rep. Christopher Murphy (D-Conn.) declared his Senate candidacy Thursday morning, a move that comes less than 24 hours after Sen. Joe Lieberman (I) formally announced his intention to retire once his current term expires in 2012.

Murphy’s announcement also comes the same week that another Democrat, former Connecticut Secretary of State Susan Bysiewicz, declared her intention to seek Lieberman’s seat, setting up a primary battle for a Senate seat that Democrats feel comfortable taking in the next cycle.

“I’ve decided to run for the United States Senate in 2012 because I believe that I can be a stronger voice for the issues that matter to Connecticut, like creating good jobs and ending these costly wars, in the Senate,” Murphy said in a statement, released the same morning his campaign unveiled a new website and a professionally produced announcement video shot largely in his home with images of his wife and young son.

See the video here: https://www.chrismurphy.com/askchris.

“This wasn’t an easy decision for me. My heart is in the fifth district, where Cathy and I are raising our son, and my top priority will continue to be doing this job that I love. I only take this step because I believe I can be an even stronger voice for change in the United States Senate,” Murphy said in the statement.

He continued: “I’m thankful for all the encouragement I have received to take this step, from family, friends, and people across the state. What I’ve heard is that people feel that the Senate simply doesn’t work anymore — it’s become an unjustifiable barrier to positive change, and Connecticut needs a fresh, progressive voice there that will push for both policy and institutional reform. “

Democratic Senatorial Campaign Committee Chairwoman Patty Murray (Wash.) offered a confident assessment of her party’s chances of winning the seat held by Lieberman since 1989.

“Democrats will win this seat next November,” Murray said. “Connecticut is one of the few states in the country that withstood fierce Republican headwinds last cycle. With President Obama at the top of the ticket and a galvanized Democratic electorate, this seat will stay Democratic in 2012.”

And while Democrats like their chances in the Senate contest, Republicans are already eyeing Murphy’s 5th district House seat, which is the most competitive district in the state, on paper at least, and was held by former Rep. Nancy Johnson, a Republican, as recently as 2006.

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

A Democratic strategist suggested that there’s no cause for concern.

“They’re laughing if they think they can put this one in play,” the strategist said. “Democrats handily survived the shellacking of 2010 here and it’s an overwhelmingly Democratic district, with the right candidate it will stay in Democratic hands.”

Meanwhile, the Democratic field for Lieberman’s seat could grow again in the coming weeks.

Rep. Joe Courtney (D) of the 2nd district is also mulling a run.

“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.