After his speech at the 2008 Republican National Convention in which he endorsed John McCain for president, he no longer attended Democratic Caucus leadership strategy meetings or policy lunches.

During debate on the Affordable Care Act (ACA), as the crucial 60th vote needed to pass the legislation, his opposition to the public health insurance option was critical to its removal from the resulting bill signed by President Barack Obama.

[20] He suffered his first defeat in Connecticut elections in the Reagan landslide year of 1980, losing the race for the third district congressional seat to Republican Lawrence Joseph DeNardis,[21] a state senator from suburban Hamden[22] with whom he had worked closely on bipartisan legislative efforts.

[28] He scored the nation's biggest political upset that year,[29] after being backed by a coalition of Democrats and unaffiliated voters with support from conservative Republicans, most notably including National Review founder and Firing Line host William F. Buckley Jr. and his brother, former New York Senator James L. Buckley,[30] who were disappointed in three-term Republican incumbent Weicker's liberal voting record and personal style.

I got a call from Erskine Bowles who was Chief of Staff about three or four days later saying that he was going to express an opinion which wasn't universally held at the White House – he thought I helped the president by bursting the boil, that was the metaphor he used.

[20] Lieberman sought the Democratic Party's renomination for U.S. Senate from Connecticut in 2006 but lost to the comparatively more liberal[43] Ned Lamont, a Greenwich businessman[44] and antiwar candidate.

[60] Democratic minority leader Harry Reid, while endorsing Lamont, promised Lieberman that he would retain his committee positions and seniority if he prevailed in the general election.

Mel Sembler, a former Republican National Committee finance chairman, helped organize a reception that raised a "couple hundred thousand dollars" for Lieberman, who was personally in attendance.

[67] When control of the Senate switched from Republicans to Democrats in June 2001, Lieberman became Chairman of the Governmental Affairs Committee, with oversight responsibilities for a broad range of government activities.

At the hearings, he pressed the United States Department of Health and Human Services to distribute vaccines and antiviral medications at a quicker pace and to streamline the process.

He emphasized the group's outreach to supporters of Hillary Clinton, who was at that time broadly expected to lose the Democratic presidential nomination to Barack Obama.

[115] Many Democrats wanted Lieberman to be stripped of his chairmanship of the Senate Committee on Homeland Security and Governmental Affairs due to his support for John McCain which went against the party's wishes.

[125] Pastor Hagee, CUFI's founder and leader, made a number of controversial remarks, including a statement that the Catholic Church is "the great whore" and a suggestion that God allowed the Holocaust to happen to bring the Jews to Israel.

[126] In April 2010, Lieberman blasted President Obama for stripping terms like "Islamic extremism" from a key national security document, calling the move dishonest, wrong-headed, and disrespectful to the majority of Muslims who are not terrorists.

[130] American computer security specialist and author Bruce Schneier objected to the "kill switch" proposal on the basis that it rests on several faulty assumptions and that it's "too coarse a hammer".

"[133] Along with Senators John Ensign and Scott Brown, Lieberman "introduced a bill to amend the Espionage Act in order to facilitate the prosecution of folks like Wikileaks.

"[134] Critics have noted that "[l]eaking [classified] information in the first place is already a crime, so the measure is aimed squarely at publishers," and that "Lieberman's proposed solution to WikiLeaks could have implications for journalists reporting on some of the more unsavory practices of the intelligence community.

[149] That same year, he joined Republican Senator Scott Brown and bipartisan House members Jason Altmire and Charlie Dent in introducing the Terrorist Expatriation Act, which proposed stripping citizenship rights from Americans who took arms against the United States or provided material support to enemy combatants.

[1] He became senior counsel of the white collar criminal defense and investigations practice at Kasowitz, Benson, Torres & Friedman, a law firm in New York City whose notable clients include Donald Trump.

[163] In order to address biological threats facing the nation, the Blue Ribbon Study Panel on Biodefense created a 33 step initiative for the U.S. Government to implement.

Lieberman headed the organization with former Governor Tom Ridge, and the Study Panel assembled in Washington, D.C., for four meetings concerning current biodefense programs.

[166] In March 2016, Lieberman was hired by the Schaghticoke Tribal Nation to assist the group in challenging Connecticut laws giving exemptions to only the top two state gaming tribes to build casinos.

One report on Lieberman's involvement was critical of him for failing to disclose in his testimony the extensive legal work his Kasowitz, Benson, Torres & Friedman law firm had done for Donald Trump since at least as long ago as 2001.

[172] The interview took place against the background of the appointment of Special Counsel Robert Mueller to investigate issues connected to Russian interference in the 2016 United States elections.

[176] On July 17, 2018, Lieberman published an opinion piece in The Wall Street Journal imploring people to vote for Joe Crowley, who was defeated in the Democratic primary by Alexandria Ocasio-Cortez.

[178] In July 2022, Lieberman became one of the founding members of a group of U.S. business and policy leaders which shares the goal of engaging constructively with China and improving U.S.-China relations.

[185] From March 2005, Hadassah Lieberman worked for Hill & Knowlton, a lobbying firm based in New York City, as a senior counselor in its health and pharmaceuticals practice.

She held senior positions at the Hospital of Saint Raphael in New Haven, the American Committee for Shaare Zedek Medical Center in Jerusalem, Association of Public-Safety Communications Officials-International (APCO), Pfizer, National Research Council, Hoffmann-La Roche, and Lehman Brothers.

[188] Matt is the former head of the school of Greenfield Hebrew Academy in Atlanta[189] and was an unsuccessful candidate in the 2020 United States Senate special election in Georgia.

[211] Lieberman authored at least 10 books, including The Power Broker (1966), a biography of the late Democratic Party chairman John M. Bailey;[212][213] The Scorpion and the Tarantula (1970), a study of early efforts to control nuclear proliferation;[214][215] The Legacy (1981), a history of Connecticut politics from 1930 to 1980;[216][217] Child Support in America: Practical Advice on Negotiating and Collecting a Fair Settlement (1986), a guidebook on methods to increase the collection of child support from delinquent fathers;[218][219] In Praise of Public Life (2000);[220][221] An Amazing Adventure: Joe and Hadassah's Personal Notes on the 2000 Campaign (2003), reflecting on his 2000 vice presidential run;[222][223] The Gift of Rest: Rediscovering the Beauty of the Sabbath (2011), written with David Klinghoffer,[224][225] With Liberty and Justice: The Fifty-Day Journey from Egypt to Sinai (2018), on a trip with Rabbi Ari D. Kahn,[226][227] and The Centrist Solution: How We Made Government Work and Can Make It Work Again (2021).