Six years ago Joe Lieberman was the darling of the Democratic Party.

In a salute to the Connecticut senator's character, moral fiber and steadfast moderation, Al Gore chose him to be the party's vice presidential candidate. That made sense, as Lieberman enjoyed many positive traits Gore lacked. Lieberman's 2000 nomination proved that the Democratic party still understood that most Americans value moderation over far-left liberalism.

On Tuesday, the Democratic Party discarded that tired old notion by ousting the pro-war, strong-on-national-security Connecticut centrist in favor of an extreme liberal anti-war Democratic challenger: millionaire Connecticut businessman Ned Lamont.

Lamont's candidacy was fueled by the most extreme elements of the Democratic party. Moveon.org, Daily Kos and other elements of the Web savvy liberal "netroots" made defeating Joe Lieberman their number one priority. To them, Lieberman was an unacceptable cancer within a Democratic party they fancy themselves as owning. Tolerance of a Democrat who was committed to finishing the job in Iraq was a non-starter. Nor was it acceptable for Lieberman to be so unabashedly pro-American in his rhetoric about national security.

This same crowd doggedly jeers Hillary Clinton for her support of the War on Terror while it cheers Jack Murtha, who once told an audience that the United States was "more dangerous to world peace than North Korea and Iran." It is the same crowd that pledges fealty to Markos Moulitsas, founder of the liberal blog Daily Kos, who once remarked he feels "nothing over the death of mercenaries" in Iraq. "They aren't in Iraq because of orders, or because they are there trying to help the people make Iraq a better place. They are there to wage war for profit. Screw them."

The "screw them" Bush-lied-people-died caucus was victorious Tuesday night.

In their victory they drove a stake through the heart of the old-school Truman-Kennedy Democratic brand of foreign policy and served notice to the entire country that this party belongs exclusively to them. Dissenters, especially those who are strong on national security and in favor of finishing the job in Iraq, need not apply.

With a result like this, you cannot blame Republicans for making some noise. Yesterday, Republican National Committee Chairman Ken Mehlman told an audience in Cleveland that this was a "sobering moment" for the Democratic Party. For Mehlman, it's a signal of the complete transformation of the 21st century Democratic party. Tuesday's results, said Mehlman, reflect "an unfortunate embrace of isolationism, defeatism and a 'blame America first' attitude by national Democratic leaders at a time when retreating from the world is particularly dangerous."

The centrist Democratic Leadership Council's Marshall Whitman also decried the trend within his party. On his blog Whitman wrote that on the issue of national security it was "regressing back to the glory days of the early seventies. In their reflexive opposition to everything Bush, Democrats too often appear weak on fighting the war against Jihadist terror." Whitman concludes that, "The only jihad many in the left-wing in the party are interested in is the one against the party's former vice presidential standard bearer."

For his part, Joe Lieberman, who has vowed to run in November as an independent, is completely cognizant of the ramifications of his defeat. In an interview with ABC the morning after the primary Lieberman commented on the callous viciousness of his opponents. "I will tell you that the bloggers who came after me -- some of them were so full of hatred ... that it is just not good for our politics," said Lieberman. "And, frankly, on some of those blogs was the kind of bigotry that just has no place in American public life. So I worry that this victory by Ned Lamont ... will send a message across our state and our country that the Democratic Party has been taken over by people who are not from the mainstream of America."

All of this is coming at a time when an anti-incumbent mood appears to be gripping the nation. A recent Washington Post-ABC news poll found that American's approval of their elected representatives has not been this low since 1994 -- the year Republicans ended the Democrat's 40-year control of the House of Representatives. If history repeats, we may see Congress controlled by a party hijacked by far-left liberals with zero commitment to national security or to waging the long war on terrorism.

Centrist Democrats committed to national security can still root for Lieberman in the general election. For them, the prospect of the far-left liberal "netroots" seizing power must be as scary as it is for many of us.

Tim Chapman is the Director of the Center for Media and Public Policy at The Heritage Foundation and a contributor to Townhall.com's Capitol Report.