Since the Vietnam war, liberalism has shifted leftward, particularly on the use of force and on the social issues that emerged in the 1970s. Today, we are confronted by another totalitarian foe, in the form of radical jihadism, and there is a need for progressive leadership that can forcefully defend America and our values.

Joe Lieberman, more than any other national Democrat, represents the JFK tradition in the national Democratic Party. Like so many others of his generation, including former President Bill Clinton, Lieberman came of age politically with the 1960 election of John F. Kennedy.

In addition to being a standard-bearer for the party's tradition of equal opportunity and upward mobility, Kennedy was a muscular internationalist who understood that force was sometimes necessary in order to protect the nation's freedom and security. As Lieberman notes: "I am a Democrat. I believe in the Democratic Party. I believe in the vision of JFK and, I must say, the vision of Bill Clinton."

That tradition is now being challenged by the left in the Democratic party. Driven by a motley coalition of left-wing bloggers and the MoveOn.org crowd, a serious primary challenge has been launched against Lieberman. However, if Lieberman is defeated, a disastrous message would be sent to the nation that centrist hawks are unwelcome in the Democratic Party.

The Connecticut Senate primary is nothing short of a battle for the soul of the Democratic Party. That is why outside left-wing groups have converged on this state.