Editor's note: Gloria Borger is a senior political analyst for CNN, appearing regularly on CNN's "The Situation Room," "Campbell Brown," "AC360°" and "State of the Union With John King," as well as during special event coverage.
Washington (CNN) -- Right now, the political intelligentsia is consumed with the outcome of a congressional district in upstate New York.
After all, it's a great story: The longtime incumbent Republican leaves his safe district to become Barack Obama's army secretary. The region's GOP pooh-bahs meet behind closed doors and pick a social moderate -- a longtime Republican assemblywoman -- to run in the special election. She slides dramatically in the polls after conservatives pitch their tents in the district to loudly oppose her. At the last minute, she quits -- and endorses the Democratic nominee.
She has been driven out of the race by the purists.
Sure, there's a lesson here for the political establishment: It's never a good idea to pick your candidate in a deal made behind closed doors.
It's also a good idea, if you're the GOP, to find someone who might be acceptable to the mainstream. Republican Dede Scozzafava, as it turns out, was not -- on cultural as well as economic issues.
In many ways, it's a unique situation. But you can be sure that won't stop the party's activists from claiming a meaningful, long-term victory against those squishy Republicans, the ones who don't take their loyalty oath in blood.
So get ready for the next big fight: McCain vs. Palin, in the Florida senate race.
On the GOP side, it's going to pit John McCain, who has endorsed Gov. Charlie Crist, a more moderate GOPer, against his former running mate, who is likely to endorse Marco Rubio. Rubio markets himself as a true conservative.
After all, Palin endorsed the conservative in upstate New York. Maybe she can see it from Alaska.
Indeed, says one longtime GOP strategist who considers himself a conservative Republican, "the New York race will embolden a segment of people on the right who are all about purging the party of heretics. If the conservative wins, their movement will metastasize."
Obviously, he doesn't see it as a healthy development. Here's why:
Independent voters make up the only truly expanding segment of the electorate. The Republican Party is a shrinking entity, down to 20 percent of the electorate at last count. One way to be sure independents do not move in your direction: use anger as an enticement to get their votes.
But get ready. It will continue to happen, no matter what the outcome in upstate New York. When a party is out of power, there's always a debate between the purists and the big-tenters.
The Democrats began theirs after Walter Mondale's loss in 1984; when they won 26 House seats in the 1982 midterm elections, they wrongly figured the party was just fine and would keep winning.
Bill Clinton had to convince the liberals they wouldn't win unless they actually had an agenda of their own to promote. He was right; Democrats only regained majority status when Clinton's Third Way started appealing to independent voters.
Sure, the world has changed since then. But the majority of voters who don't like angry politics on either side is only growing.
As no greater conservative source than the editorial page of The Wall Street Journal reminds us, "The Democrats did themselves no favor by driving Joe Lieberman out of their party, and conservatives will do their cause no good by forcing GOP candidates in Illinois, California and Connecticut to sound like Tom DeLay.
"If conservatives now revolt against every GOP candidate who disagrees with them on trade, immigration or abortion, Nancy Pelosi and Harry Reid will keep their majorities for a very long time."
Not to mention keeping Barack Obama in the White House.
The opinions expressed in this commentary are solely those of Gloria Borger.