Sen. Joe Lieberman (I-Conn.) was clearly frustrated with some in the Democratic Party who rallied strongly for Ned Lamont in the 2006 general election.

Lieberman knew that the Democratic establishment had to back Lamont after the anti-war Democrat triumphed in their 2006 primary showdown. But some went further, and it rubbed Lieberman the wrong way.

Sen. Chris Dodd (D), Lieberman’s Connecticut colleague in the upper chamber, said at the time he did not approve of Lieberman’s decision to run in the general election. Sen. John Kerry (D-Mass.) put out a statement in the wake of Lieberman’s loss, calling for Democrats to unite behind Lamont.

Lieberman said it hurt him personally to “see some of my friends in the Senate turning to Lamont.”

He went on to defeat Lamont easily in the general election, and asked the Senate to refer to him officially as an “Independent Democrat (ID).”

Senate Majority Leader Harry Reid (D-Nev.) wisely gave Lieberman the gavel of the Homeland Security and Government Affairs Committee at the start of the 110th Congress. If he had not, Reid was well aware, the chances of Lieberman caucusing with Republicans — which would have shifted control of the Senate — would have increased exponentially.

The Lieberman saga is far from over. He has endorsed Sen. John McCain (R-Ariz.) for president and, as The Hill’s Manu Raju reports, is not ruling out being the keynote speaker at the Republican National Committee Convention (RNCC) this summer.

It is unclear if McCain will ask the 2000 Democratic vice presidential nominee to deliver the keynote, but it’s a possibility. McCain won the Republican nomination in part because the U.S. troop surge improved the situation in Iraq.

Lieberman agrees with McCain on the war, as well as on some other issues, such as global warming.

On a variety of other matters, they do not agree, so it is unlikely that, despite the speculation, McCain would ask Lieberman to be his vice president.

Much of the left despises Lieberman. Breaking with party leadership, especially on who should be the next president, will attract many critics.

Lieberman is in a unique position to disregard party politics because he doesn’t belong to one anymore. In 2007, he contributed $100,000 to the Democratic Senatorial Campaign Committee.

Meanwhile, his political action committee has given to Sens. McCain, Max Baucus (D-Mont.), Susan Collins (R-Maine), Tim Johnson (D-S.D.), Mary Landrieu (D-La.) and Mark Pryor (D-Ark.).

Other than Pryor, who was not in the Senate in 2002, all of those senators voted for the Iraq war.

A Lieberman keynote address at the Republican convention in Minneapolis would be viewed by many Democrats as a major offense. It would draw immediate comparisons to the spirited and scowling address by then-Sen. Zell Miller (D-Ga.) at the 2004 GOP convention. Lieberman has made it plain that he believes McCain is the best presidential candidate, and there doesn’t appear any limit to how far he will go to remind voters of his opinion.