Sen. Arlen Specter ended 29 years of speculation by finally leaving the GOP and joining the Democratic Party. The Pennsylvanian’s career has swerved, turned, zigged and zagged, teetering back and forth between political parties over the years. But it appears that Mr. Specter has finally gone back to where he belongs.

Liberals in the Republican Party are caterwalling. The media, grimly declaring the “big tent” has vanished, predict the death of the Republican Party. Without moderates, they say, Republicans are doomed. In reality, the conservative people of Pennsylvania have accomplished a great deal by forcing Mr. Specter to change parties.

Defection is a difficult, risky, and costly move. While Republicans controlled the Senate, Mr. Specter’s seniority entitled him to chairmanship of whatever committee he desired, and control of the agenda of that committee.

Senate committees work in an odd way: nominees or laws can be “bottled up in committee” as long as the minority party gives up no votes to the majority. As a member of the minority, Mr. Specter had the power to give up that one, all-important vote, allowing liberal laws and nominees to move onto the floor for affirmation. Whether committee chairman or member of the minority, he effectively drew attention, concern and power to himself as other Republicans modified their stands to mollify him. As a Democrat, he’s now lost that power.

People sometimes vent their frustration with existing politics by investing hope in the creation of a third party, but historically, third parties only divide the vote. A politician like Mr. Specter holds a party hostage to the exercise of his own power. Mr. Specter’s jump to the Democrats loosens his grip on Republicans and may alleviate this frustration.

Ideas require physical space in which to operate. Limited government and freedom found their most perfect expression in America. The great ideological conflict we call the Civil War was based on the conflicting ideas of two major physical places.

Pennsylvania is thought of as a dependably liberal state. Republicans have difficulties winning elections there. It’s one of the least likely locations of the resurgence of the conservative movement—making it even more remarkable that the people of Pennsylvania have taken the lead. No politician gives up power willingly; he must be made to walk the political plank. In these days of piracy, the Pennsylvanians have taken back their ship.

Mr. Specter will actually cause Democrats problems. He’s been promised that his seniority in the Republican Party will be transferred intact, enabling him to displace established Democratic senators. Surely this will cause dissention among these power-seeking politicians. Mr. Specter did not move because he feels more comfortable in the Democratic Party but because conservative voters made him less comfortable in the Republican Party. Republican Pennsylvanians have effectively rid themselves of a manipulative and subversive politician.

Should Mr. Specter win the general election next year, he will continue to pose problems for Democrats. If he loses the nomination, then he’s gone—good riddance. If, against conventional wisdom, Pat Toomey wins, a successful cleansing of the party will have begun. The Republicans as a “me, too” party will recede. If voters in other states take heart from Pennsylvanians and follow suit, a true opposition party will rise up.

Legitimate concerns have been raised. Republicans could continue as a minority. Losing an entire geographical region to the Democrats is not desirable. However, Republicans from the northeast have tended to go along with Democrats anyway. When Republicans were in the majority, politicians like Mr. Specter weakened conservative principles, eventually undermining the party.

Like a woman who finally decides to rid herself of a faithless husband, rejecting advice from relatives and friends to try to work it out, Republicans need to move on. That woman may never find another man, but she’s better off free of the negative association. Likewise, a Republican minority, secure in their own beliefs, are better off than a diffused majority constantly in danger of being overthrown.

Pennsylvanians can take pride in the fact that what may be the beginning of a return to limited government and renewed responsibility of politicians to their constituencies began with their ability and willingness to express their feelings clearly and forcefully.