Joe Lieberman is a heretic. Please don’t get me wrong. Nobody, not even Lieberman’s enemies, questions the Connecticut Senator’s abiding Orthodox Jewish religious faith. But as Tuesday’s primary election shows, a majority of Nutmeg State Democrats see their senator as disloyal to the party line, which is increasingly dovish on Iraq. And a heretic, of course, is much worse than an infidel.

So Lieberman had not only to be defeated, but to be crushed and vilified. Which he was. Lieberman supporter Lanny Davis detailed in the pages of The Wall Street Journal all "the hate and vitriol of bloggers on the liberal side of the aisle" that poured down on his candidate, including scurrilous anti-Semitism.

Here’s the distinction: An infidel is someone who never believed what you believe; an infidel is a stranger, and so there’s not much point in investing emotions in him. But a heretic is someone you know well, someone who once believed what you believe, but now has a different faith -- that’s much more threatening. You often fight wars against infidels, and in those wars you seek to defeat, even destroy, the enemy. But with heretics, even tougher measures are needed, because the threat of heresy is so much more insidious, threatening to eat away the true faith. So you launch inquisitions against heretics, to eliminate even the thought of heresy. The proper anti-heretical strategy is to torture ‘em, make ‘em confess, make ‘em repent -- and then kill ‘em.

Happily, American politics isn’t nearly so brutal, albeit still intense. And yet the basic heretics vs. infidels dichotomy explains why intra-party fights are so much more bitter than inter-party fights. To this day, for example, the Democrats know Which Side They Were On in big intra-party feuds -- even if they were too young actually to have been part of the feud.

We might consider, for example, one epochal feud-year for the Democrats: 1948. That was the year that lefty Democrats split off from the party, and from President Harry Truman, to join the pro-Soviet third-party candidacy of former vice president Henry Wallace. Six decades later, that sundering still echoes; The New Republic’s Peter Beinart, himself born in the '70s, published a book that revisits 1948. Its militant title, The Good Fight: Why Liberals -- and Only Liberals -- Can Win the War on Terror and Make America Great Again, signals Beinart’s message for today: that the fight against hawkish heretical Democrats has gone too far -- and that the answer is to fight right back. He wants Democrats to draw inspiration from past struggles, from the days when Cold War liberals battled crypto-communists. And so Beinart supported Lieberman, of course, against the primary campaign waged against the incumbent by challenger Ned Lamont. Needless to say, Beinart’s left-bashing has been reciprocated by plenty of Beinart-bashing from lefties, including The Nation’s Eric Alterman. And so the guns of 1948 are still not silenced, and the wounds are still open.

To further underscore the bitterness of intra-party squabbles, it’s worth remembering that there was actually a second breakaway campaign from the Democrats in 1948, and people still remember that split, too. Gov. Strom Thurmond, Democrat of South Carolina, outraged by Truman’s "progressive" civil rights platform, bolted the party and ran for president in a few Southern states on the segregationist "Dixiecrat" ticket. Young Trent Lott, growing up in a Democratic household in Mississippi, was all of six years old when Thurmond stormed out of the Chicago Democratic convention, but he still remembered that moment in 2002, when he destroyed his own career as Senate Majority Leader by heaping praise on Thurmond’s ‘48 candidacy. Lott has long been a Republican, of course, but his memories of the long-ago War Between the Democrats obviously remained with him, more than a half-century later, still strong and vivid. (Interestingly, in spite of having two intra-party rivals, Truman won a second White House term -- a reminder that intra-party squabbling, while deeply engaging to activists, is not what the country cares most about.)

Another hinge-year for Democrats was 1968, when the anti-war insurgency within the party knocked over President Lyndon B. Johnson as he sought re-nomination and re-election. Lots of conservative Democrats -- the soon-to-be "neoconservatives" -- were so mad as a result that they left the Democratic Party, whereupon the triumphant insurgents heckled "good riddance" at them.

Nor are Republicans spared such intra-party intensity in which heretics are purged. The banner years for GOP feuding include 1964 and 1976. In ‘64, Sen. Barry Goldwater’s conservatives vanquished Gov. Nelson Rockefeller’s moderate-liberals, beginning the Sunbelt-ization of the GOP. And in ‘76, Ronald Reagan’s near-upset of an incumbent Republican president, Gerald Ford, set in motion the conservative takeover which holds on to this day; that divisive campaign is lovingly detailed by Reaganite Craig Shirley in his book Reagan’s Revolution: The Untold Story of the Campaign That Started It All.

And now, back to the 2006 Democrats. Angry donkeys in Connecticut have purged one of their most popular leaders in a blogosphere-led campaign; the proverbial Army of Democratic Davids have knocked off a Democratic Goliath.

And while Lieberman is notoriously restrained and polite, his own strong feelings about his fellow Dems were visible in the wake of his defeat, as when he said on CNN that Lamont’s wing of the Democratic party could "not give assurance to America that we will do what has to be done to protect us from terrorists." Republicans are lapping up such rhetoric, of course, but it’s Democrats who are carrying on the fiercest fight -- against each other.

Here’s a typical headline bespeaking internecine intensity: "The Sweetness of Lieberman’s Defeat." And reacting to the candidate’s announced decision to run as an independent, the blog Daily Kos sniped, "Now, Lieberman wants to stab his allies and his party in the back. It won’t be the first time." And Arianna Huffington joined in the blog-slaught on Wednesday, decrying "Joe Lieberman’s selfish, self-serving, spoiled-rotten attempt to undercut Ned Lamont’s historic victory." Then she added, twisting the knife, that Lieberman’s third-party run will further undercut the Democrats’ chances of retaking Congress in November. Them’s fightin’words.

And here’s another heretic-burner, Michael Moore, waving around his torch, casting fiery light into the future: "To every Democratic Senator and Congressman who continues to back Bush’s War, allow me to inform you that your days in elective office are now numbered. Myself and tens of millions of citizens are going to work hard to actively remove you from any position of power." Once again, we know that Michael Moore-types dislike the Republicans across the aisle, but they reserve a special ferocity for those on their side of the aisle.

And the beat -- make that the beating -- goes on. Looking ahead to the 2008 Democratic presidential nomination, pollster Dick Bennett recently shared with The Boston Herald some of the "verbatim" comments he had heard about Hillary Clinton: "lying bitch ... shrew ... Machiavellian ... evil, power-mad witch ... the ultimate self-serving politician." And here’s the kicker: All these comments were from Democrats, most of them angry about the New York Senator’s nuanced support for the Iraq war. "I thought there might be some negatives, but I didn’t know it would be as strong as this. It’s stunning," summed up Bennett.

So far, at least, the "infidels" in this particular Demo-drama, aka the Republicans, can sit back and enjoy the heretic-burning show. But GOPers should be mindful that the same "purifying" process, as we have noted, regularly occurs in their party, too. Is every Republican happy with the Iraq war? Or with hardshell social conservatism? No? Great! Time for a purge! Let’s root out those "RINO’s" -- Republicans In Name Only. That’s what happened to Joe Schwarz on Tuesday.

It didn’t get much attention, but on the same day that Lieberman lost his Connecticut primary, Schwarz, a moderate Republican Congressman, was defeated in his Michigan primary. Schwarz had been endorsed by George W. Bush, John McCain, and the National Rifle Association, but that wasn’t good enough for GOP voters of the 7th District; he was "impure" on the issues of abortion and stem cell research. As one centrist Michigan observer told The Detroit Free Press, "It seems pretty clear that the extreme right wing was highly motivated and turned out." Speaking in the apocalyptic language that comes comfortably to heretics-busters, conservative activist Gary Bauer declared of the Michigan race, "The right to life and traditional marriage are not wedge issues, they are winning issues. Values issues are not distractions from the business of governing. They are central to the survival of our republic."

Joe Lieberman must know exactly how Joe Schwarz feels. As the AP headline atop Tuesday’s news explained, "Activists Targeted Political Moderates." That is, in both parties, the same thing was happening: base-loyalists purged the heretics on the margin. And if that means that the infidels -- the folks in the other party -- are more likely to win the general election, well, that’s the price one pays for party purity.

It’s deeply satisfying to true believers to practice such "ideological cleansing." And if such behavior is embedded in human nature, it’s not about to change. But the challenge to political professionals is to keep their eye on the big picture -- the November elections. Victory, defined as actually winning office, will come to the party that spends less time searching out heretics, and more time figuring out how to defeat the infidels.