Lieberman represented Connecticut in the United States Senate as a Democrat, and was the party’s vice presidential nominee when he ran with Al Gore against George W. Bush in 2000. In 2006, he became an independent when he lost the Democrat primary for his Senate seat, and subsequently won re-election.
Known for his tough stance on terrorism, Lieberman endorsed John McCain over Barack Obama in 2008. He retired from the Senate in 2013, and has been in private law practice since.
In spite of his national security bona fides, Lieberman has no experience with law enforcement and was considered a long shot to replace James Comey, who was fired from the FBI by Donald Trump. That firing has been an ongoing source of controversy.