Last week's defeat of Sen. Joe Lieberman in Connecticut's Democratic primary is being treated as a purge by both Democrats and Republicans. Those on the Democratic Party's left wing are hoping that it will send a signal throughout the party that opposition to the war in Iraq is absolutely mandatory for all Democrats. Republicans will hammer home the idea that Democrats are no longer willing to tolerate internal dissent on this issue even from someone who was the party's vice presidential nominee just six years ago.

This is not the first time the Democratic Party has mounted a purge of those viewed as being to the right of its left-wing base. In 1938, President Franklin D. Roosevelt set out to personally purge the party of any congressman or senator unwilling to support every New Deal program down the line, no questions asked. It proved to be the first step in weaning the "Solid South" away from the Democratic Party and putting it into the Republican column.

Before the Civil War, the Democratic Party was the party of slavery, fighting every congressional effort to end that awful institution. The Republican Party was created for the express purpose of ending slavery, which the Whig Party was too frightened to take a position on. After the war, Democrats fought enactment of the 14th and 15th amendments to the Constitution, and in every Southern state they enacted "Jim Crow" laws to keep blacks down and reinstitute de facto slavery through chain gains, peonage laws, lynching and disenfranchisement.

Republicans fought these efforts, passing many civil rights laws that ended up being invalidated by the Supreme Court. It would be almost a century before the Court's philosophy changed and allowed similar laws to be enacted in the 1960s.

Republicans also fought Democratic efforts to re-impose de facto slavery in the South after the war, but it required federal military occupation to protect the rights of blacks -- something that could not be maintained indefinitely. After the withdrawal of federal troops in 1877, racists retook control and kept the South firmly in the Democratic column for the next 100 years.

Roosevelt tried to break the power of the Southern conservatives by openly campaigning against many of them in 1938. But his effort was a total failure. For example, in Georgia, Roosevelt's opposition to Sen. Walter F. George boomeranged and probably ensured his re-election. Georgians didn't much care for outsiders telling them how to vote -- even a president they had supported overwhelmingly in 1932 and 1936.

As a result of the failed purge, Roosevelt found his power in Congress substantially diminished after 1938. Southern Democrats were increasingly willing to oppose him, even joining with Republicans to do so. By 1948, many Southern Democrats broke with the national party, voting for the so-called Dixiecrat candidate, instead. In 1964, they voted for Republican Barry Goldwater for president -- probably the first time many had ever pulled the Republican lever.

Despite growing alienation from the national Democratic Party, Southern states still consistently voted Democratic in virtually all House and Senate races. The reason was that many Southern Democrats held powerful positions in Congress as committee chairmen who could deliver pork and other federal goodies to their constituents.

But Northern Democrats were embarrassed by their Southern brethren and their racist past. After winning huge majorities in Congress in 1974 and 1976, they mounted a purge of Southern Democrats, removing many from committee chairmanships. At this point, the Southerners had nothing left to be gained by being Democrats.

In the 1980s, Republicans started making a serious effort to win elections in congressional and state races throughout the South. They recruited good candidates, financed them well, and emphasized over and over again the disdain that Northern Democrats had for those in the South. By 1994, the Democratic Party was decimated throughout the South, contributing powerfully to the Republican takeover of Congress that year.

From this history, it is clear that past Democratic purges have only had the effect of aiding the Republican Party. I suspect that the purge of Sen. Lieberman may have the same effect, possibly turning what might have been solid gains by the Democrats in this fall's elections into modest gains. There are lots of Democrats who think like Sen. Lieberman on Israel and Iraq. They now have no choice but to vote Republican.

Historically, the American people have often supported candidates they believed were motivated by genuine conviction, even when those convictions were out of step with most of their beliefs. Americans like men of principle and dislike those who are merely pandering to momentary passions. For this reason, I think Sen. Lieberman will triumph in November, running as an independent. It won't surprise me if this latest Democratic purge ends up helping the Republicans once again.