On Tuesday night, President Obama walked down the aisle of the House of Representatives, en route to deliver his first speech to a joint session of Congress, shaking hands of Republican and Democratic members.

He saw Sen. Joe Lieberman of Connecticut, an Independent who caucuses with the Democrats, shook his hand and then hugged him. This despite Mr. Lieberman's support for the Republican, Sen. John McCain of Arizona, in the fall election.

Two days later, a group of self-described liberal bloggers, backed by a major labor union and MoveOn.Org, announced a new political action committee called "Accountability Now."

According to a New York Times report, the group planned on raising money to recruit "liberal candidates for challenges against more centrist Democrats currently in Congress," such as the more middle-of-the-road House "Blue Dog Democrats" (even though virtually all them supported the Obama stimulus bill).

The founders are some of the same folks who made a huge deal on the blogosphere out of Lieberman allowing himself to be kissed on the cheek by then-President Bush when Bush was walking down the same aisle in the House to deliver his 2006 State of the Union speech.

During the 2006 Democratic primary in Connecticut, supporters of Lieberman's opponent, a former Republican named Ned Lamont, egged on by these same bloggers, built a papier-mâché model of "The Kiss" to rev up anger against Lieberman by anti-Bush Connecticut Democratic voters.

The irony for me, seeing "The Hug" as a Lieberman friend and supporter who remembered the viciousness of "The Kiss" issue used against him in the primary, was — well, to be completely honest — delicious.

These two events — "The Hug" and, two days later, the announcement of this new "Accountability Now" group — may not seem significant in the great scheme of things. But they may actually signify a serious philosophical divide within the Democratic Party.

On one side are President Obama and other traditional liberals who are committed to progressive policies but who know that the Democratic center and Republican middle-of-the-roaders are necessary to build an enduring governing coalition for fundamental change in the country.

On the other side are certain bloggers and groups who call themselves liberals but whose objectives, as stated to the Times, seem to be the ideological cleansing of the Democratic Party — eliminating anyone who doesn't meet their definition of liberalism on every issue.

The Obama hug, therefore, emblemized this philosophical difference.

It wasn't the first time Mr. Obama had reached out to Lieberman. Recall that during his transition period, the president-elect recommended to Senate Democrats that they neither oust Lieberman from their caucus nor severely discipline him for his endorsement of McCain. This recommendation was criticized by many liberal bloggers and some of the liberal cable hosts and guests, such as MSNBC's Rachel Maddow.

But Obama's recommendation concerning Lieberman was quickly vindicated. Just days before "The Hug," Lieberman had provided his crucial vote in support of Obama's economic stimulus bill. Perhaps more importantly, he worked closely with his friend, Maine Republican Sen. Susan Collins, who helped Obama get over the magic number of 61 votes to pass the legislation.

I waited for Maddow, whose articulate and forceful voice for liberal positions I often appreciate, to concede that perhaps Lieberman had come through for Obama and the Democratic Party , and thus, she had been wrong about wanting him ousted from the Democratic caucus. I am still waiting.

Once again, Obama has proven that he is a man who says what he means and means what he says. He truly stands for a new politics, in which differences of opinion are tolerated — even the endorsement of one's political opponent can be quickly forgiven, when the objective is true change and a broad new governing center to overcome the stale "red" vs. "blue" polarizing divisions of the last 15-20 years.

Sometimes you have to wonder whether people are liberals just because they describe themselves that way. Someone who seems to be on the opposite end of the spectrum from Obama's new politics is one of the founders of the "Accountability Now" group, Jane Hamsher.

Hamsher is the creator of what is called a liberal blog, with the odd name FireDogLake.com. She is the same person who, in August 2006, posted an anti-Lieberman commentary on the Huffington Post accompanied by a doctored photo of Lieberman in blackface (standing next to President Clinton, wearing dark sunglasses).

When blacks and others expressed offense at the use of this historically racist caricature, Hamsher issued what can kindly be called a classic non-apology apology.

She wrote: "I sincerely apologize to anyone who was genuinely offended by the choice of images accompanying my blog post today on the Huffington Post." As blogger James Joyner, on his Outside the Beltway blog, noted at the time about the Hamsher "apology":

"So she doesn't think she's actually done anything wrong here but, hey, if you're offended — but only sincerely offended, not just somewhat offended — she's sorry you're so stupid to be offended."

So this is one of the leaders of the group that will determine who is a true "liberal" and which congressional Democrats should be challenged in primaries. If anyone doubts that there is a danger that this group will be more interested in revenge than in winning elections, the New York Times reporter unwittingly made the point best with two sentences in his report on the group:

"Left–leaning bloggers have already proven themselves influential in congressional races, most notably providing muscle for the movement that helped Ned Lamont defeat Senator Joseph Lieberman in the Connecticut Democratic primary in 2006. (Lieberman went on to retain his seat after running in the general election as an independent.)"

There you have it: The "left-leaning bloggers" showed "muscle" when they won a primary. And, parenthetically — oh, by the way — they lost the general election. Whatever.

That is not a recipe for change you can believe in. It is more like a recipe for the politics of vitriol, revenge and defeat, with a return to power by conservative Republicans.

We need pressure from the left in our party to remind us why we chose to be Democrats rather than Republicans. I credit organizers of Accountability Now if that is their goal. But unfortunately, their rhetoric, at least out of the box, seems more about revenge and enforcing their notion of liberal purity and ideological cleansing than helping President Obama create a new politics, fundamental changes in this country and a governing majority for years to come.