Sen. Joe Lieberman (ID-Conn.) took center stage Wednesday in the GOP’s mounting attacks on the presumptive Democratic presidential nominee, Sen. Barack Obama (Ill.), fueling talk in the Democratic Conference about his split loyalties.

Lieberman participated in a media conference call organized by House Chief Deputy Minority Whip Eric Cantor (R-Va.) to criticize Obama’s Middle East policy. Lieberman is a staunch supporter of Israel, and Republicans aim to make inroads into traditionally Democratic Jewish voters by suggesting that their presumptive nominee, Sen. John McCain (Ariz.), is a stronger Israel supporter.

Lieberman’s criticism came in response to Obama’s speech before the American Israel Public Affairs Committee, where he pledged support to the Jewish state. It was his first major address after claiming his party’s nomination late Tuesday night. Lieberman harshly criticized Obama’s speech and his broader foreign policy stance, particularly on Iran and his opposition to legislation listing the Iranian Revolutionary Guard as a terrorist group. Lieberman and Senate Minority Whip Jon Kyl (R-Ariz.) sponsored that bill.

Lieberman, who is estranged from Senate Democrats on the Iraq War, has endorsed McCain, but he went further Wednesday by criticizing Obama. While Lieberman’s comments ticked off Democrats, it is all but certain he will see no repercussions until after the election.

“There’s zero chance” that Senate Democrats will take punitive actions against Lieberman before the election, one longtime Democratic aide predicted, noting that to do so likely would put the chamber in Republican hands and could have a negative effect not only on Obama’s campaign but on Senate races as well.

But the incident appeared to have an effect on Obama. During a Senate vote Wednesday, Obama dragged Lieberman by the hand to a far corner of the Senate chamber and engaged in an intense three-minute conversation.

While it was unclear what the two were discussing, Obama literally backed up Lieberman against the wall, leaned in close and appeared to be trying to dominate the conversation, as the two talked over each other in a few instances.

Still, Obama and Lieberman seemed to be trying to keep the back-and-forth congenial as they both patted each other on the back during and after the exchange.

Afterward, Obama smiled and pointed up at reporters peering over the edge of the press gallery for a better glimpse.

Obama loyalists expressed their frustration with Lieberman’s decision and warned that if he took a lead role in attacking Obama, it could complicate his relationship with the caucus.

“It’s a difficult situation,” Senate Majority Whip Dick Durbin (D-Ill.) said on Wednesday. “Joe is my friend … but I hope he doesn’t become the lead attack dog. … Of course it’s a concern when someone in your caucus is supporting the other party’s candidate. Let’s not try and sugarcoat it.”

While Lieberman declined to say whether he would act as a surrogate for McCain in attacking Obama, he said he would not put his work in Congress in jeopardy by participating in the McCain campaign.

“Obviously I support Sen. McCain … but I can only do so much as long as it doesn’t interfere with what I’m doing here,” Lieberman said.

Asked whether his activities could endanger his role as chairman of the Senate Homeland Security and Governmental Affairs Committee, Lieberman said, “that’s up to my colleagues.”

Lieberman’s status in the Democratic Conference has been shaky since the former-vice presidential nominee left the party to become an Independent Democrat in 2006. The move was reinforced when Lieberman endorsed McCain for president and began actively campaigning and raising money on his behalf. Lieberman later said he would be willing to speak at the Republican National Convention in Minneapolis.

Publicly, Democratic lawmakers declined to say whether they thought Majority Leader Harry Reid (D-Nev.) would punish Lieberman. But privately, aides insisted that Lieberman’s Democratic colleagues would not let the incident to fade into the background once the election is over.

“There is rising concern within the caucus,” said a senior Democratic Senate aide. “It is fair to say Members also are livid with his actions this morning. Many felt he truly did cross the line, but it remains to be seen what, if anything, might be done in a closely divided Senate.”

“He crossed the line when he went negative on Obama and not just positive on McCain,” one aide said. “This is unforgettable behavior. This will be in his obituary.”

Reid has waded gingerly into the subject, given that the two Senators have long been friends. Three weeks ago during an interview with Keith Olbermann on MSNBC, however, Reid left open the possibility that Lieberman’s status as a committee chairman might not be secure indefinitely.

Reid, pointing out the Democrats’ narrow majority in the Senate and Lieberman’s support for the war in Iraq, said, “the facts are that we’re going to watch very closely.”

While Senators and aides alike did little to contain their discontent with Lieberman’s attack on Obama, Reid kept his thoughts under wraps. Reid spokesman Jim Manley declined to comment, referring only to Reid’s May remarks about Lieberman’s status on Olbermann’s show.

Lieberman loyalists, such as Sen. Lindsey Graham (R-S.C.), said the Connecticut Senator’s comments shouldn’t be surprising given his unabashed support for McCain’s candidacy. Graham said Lieberman has shown the courage to put principles over politics, regardless of the consequences.

“I think it goes to the very approach of Joe Lieberman — he’s done something people in this body don’t do very often, which is risk your career,” Graham said.

Graham said that for Lieberman, it comes down to his steadfast belief that the war in Iraq must be won.

“I really do believe it’s appropriate for Lieberman to speak his mind, and he’s earned it,” Graham said. “Obama should listen to some of those criticisms. My feeling is Sen. Lieberman understands the war on terror is the defining issue of America. It means more to him than political alliances or friendships.”

Lieberman earlier raised eyebrows among his Democratic colleagues who wondered how he would handle himself once the general election rivalry had been set. Some have asked privately whether Lieberman would continue to participate in Senate events and strategy sessions, especially since presidential politics are bound to come into play.

Sen. Sheldon Whitehouse (D-R.I.), while not familiar with Lieberman’s remarks on Wednesday, said there shouldn’t be a conflict as long as they don’t “interfere with his support or commitment to Democrats” on the floor and in terms of the agenda. “I think people around here get pretty good at separating politics from what we do here on the floor.”

Lieberman isn’t without a solid bloc of Democratic friends. Even during his divisive primary battle in 2006 that prompted him to bolt the party, many of his moderate colleagues stuck by his side. And up until the latest dust-up on Wednesday, many continued to pledge their loyalties.

Sen. Ken Salazar (D-Colo.) said last month that despite Lieberman’s decision to back McCain in 2008, “he is a Democrat in his heart and he will always be welcome as a Democrat in my state and in my house.”

Salazar said it would be up to Lieberman to decide how to navigate his politics going forward, such as whether he continues to participate in Democratic Conference meetings or other forums. Lieberman has typically opted against taking part in sessions involving the party’s Iraq War strategy since he sides with the GOP on the issue.

“He’s an integral part of the caucus and supports us 90 percent of the time,” Salazar said. “For me, it’s very comfortable having him around.”

Nevertheless, Democrats said his work for McCain is putting a strain on their Conference. “It’s hard for us,” said Sen. Claire McCaskill (D-Mo.). “It’s hard for us to see him working as hard as he is for the Republican nominee. I’m just acknowledging the obvious.” Asked whether the incident could lead to Lieberman losing his chairmanship, McCaskill said that remained unclear.

“I don’t know. … I have no idea about what is going to happen. I think a lot of it depends,” she said. “What we’re all focusing on is not who is going to be chairman next year but is how many Senators we’re going to elect next year and making sure we elect President Obama.”

Tim Taylor contributed to this report.