Senate Majority Leader Harry Reid (D-Nev.) faces mounting pressure to strip Sen. Joe Lieberman (ID-Conn.) of his chairmanship in the wake of Lieberman’s decision to attack Democratic presidential nominee Sen. Barack Obama (Ill.) in a speech Tuesday at the GOP convention.

“Joe Lieberman is a Democrat and an important member of our caucus until Nov. 5,” one Senate Democratic aide said. “The only thing that would keep Joe Lieberman afloat is if we picked up enough seats to get to [a filibuster-proof] 60 [votes] and he’s 60th.”

Any decision to deny Lieberman the gavel of the Homeland Security and Governmental Affairs Committee is unlikely to be made until after the November elections.

Lieberman was already in hot water with his colleagues for his continued support of the Iraq War and of Sen. John McCain (R-Ariz.) over Obama. But many Democrats said the self-proclaimed Independent Democrat cemented his pariah status in Democratic circles by ignoring the personal pleas of fellow Senators — including from Reid — and speaking in St. Paul, Minn., this week.

Adding to his troubles, Democrats said, is that Lieberman also disregarded warnings from Democratic leaders to keep his remarks focused on McCain’s attributes and not Obama’s deficiencies. Lieberman called Obama “a young man” and said his “eloquence is no substitute for a record, not in these tough times for America.”

Democrats said Senators who reached out to Lieberman were taking the perceived betrayal personally because they had been led to believe he would not take a harsh tone in his support for McCain.

Reid has repeatedly avoided questions about retribution against Lieberman, saying Lieberman votes with Democrats on most issues outside of the Iraq War. However, several Democratic sources confirmed this week that Reid would re-evaluate Lieberman’s chairmanship and seniority after the election, when Democrats expect to pick up at least four or five seats. Currently, Lieberman represents the one vote Reid needs to continue on as Majority Leader, given Democrats’ 51-49 majority in the chamber.

“I think people feel a lot more at liberty to speak more freely” about replacing Lieberman atop the Homeland Security Committee as well as potentially revoking his seniority on other panels, said another Senate Democratic aide following the speech. “He himself opened the floodgates here.”

Even Republicans acknowledged that Lieberman put his career on the line Tuesday night. “I thought that ranked high in political courage because you know he may pay a price for it in the United States Senate in terms of retaliation,” National Republican Congressional Committee Chairman Tom Cole (Okla.) said. “He certainly will become an even more intense focus of Democratic grass-roots’ disdain. And he did it all because he thought it was the right thing to do for his country. So I admire it. I’m not sure I’d have the courage to do it myself, to tell you the truth.”

If Democrats decide to penalize Lieberman, it would amount to a stunning fall for a man who just four years ago sought the Democratic nomination for president and eight years ago was the party’s vice presidential nominee.

His unwavering support for the Iraq War largely caused Lieberman to lose his primary in 2006, and he returned to the Senate having won election as an Independent and feeling even stronger about blazing a contrary path in the chamber.

Lieberman endorsed McCain’s candidacy in December 2007, when the field of Democrats in the presidential primary was still crowded with foreign policy authorities, such as vice presidential nominee Sen. Joseph Biden (Del.) and Sen. Chris Dodd (Conn.). None of them, however, shared Lieberman’s steadfast support for the Iraq War.

“After all of his election troubles, it was the Democrats that embraced him and brought him back into the fold and made sure he had a chairmanship,” the second Senate Democratic aide said. “He abused the trust and power he was given.”

To shore up his Democratic bonafides, Lieberman has given a whopping $230,000 to the Democratic Senatorial Campaign Committee in the 2008 election cycle, and he reasserted his status as a Democrat shortly after his speech Tuesday night. “That’s perhaps what was unique about tonight. I remain a Democrat. I disagree with the direction of [my] party. I want to stay and fight,” he told MSNBC.

Even so, Reid was highly critical of Lieberman’s speech. “Sen. Reid was very disappointed in Sen. Lieberman’s speech tonight, especially when he appeared to go out of his way to distort Sen. Obama’s record of bipartisan achievements in the Senate. He can give all the partisan speeches he wants, but as the American people have made very clear, the last thing this country needs is another four years of the same old failed Bush/McCain polices of the past,” Reid spokesman Jim Manley said.

If Democrats decide to replace Lieberman atop the Homeland Security Committee, the change would be made by the Democratic Steering Committee. Ultimately, Reid would be the decision maker, considering he appoints Members to the Steering Committee.

Technically, Lieberman would not be removed from the chairmanship. Instead, he would simply not be reappointed, aides said. The Steering Committee also could decide not to recognize his seniority on other panels and could even decline to appoint him to any committee slots.

Next in seniority to Lieberman on Homeland Security are two other chairmen — Armed Services Chairman Carl Levin (D-Mich.) who is unlikely to give up his post, making Veterans’ Affairs Chairman Daniel Akaka (D-Hawaii) next in line. If Akaka declined the slot, the chairmanship would fall to Sen. Tom Carper (D-Del.).

Of course, if McCain wins the presidential election, Lieberman is likely a top pick for Homeland Security secretary or Defense secretary. That scenario would short-circuit any effort to retaliate against him.

Asked if Lieberman would switch parties following a party reprisal, his spokesman said, “We’re not commenting on hypotheticals right now.”

But Republicans in St. Paul said they would welcome the otherwise liberal Connecticut Senator.

“We have Republican Members who have a wide variety of views. I hope our party continues to be attractive to people with Sen. Lieberman’s views,” said Senate Republican Conference Chairman Lamar Alexander (Tenn.), who noted that he had not lobbied Lieberman to switch.

“That would be totally up to Sen. McConnell,” Alexander said, referencing the Minority Leader.

Alexander predicted that if Lieberman left the Democrats, it would be because his party left him, not the other way around.

“He didn’t trash the Democrats. They defeated him,” Alexander said, referring to Lieberman’s primary defeat in 2006. “He’s a free agent, I think. He’s earned his right to be an Independent, and that was the choice of the Democratic Party.”

Lauren W. Whittington and Steven T. Dennis contributed to this report.