For much of the campaign season, Barack Obama had a sizable lead because he energized the Democratic base and pledged to bridge the gap between “red states” and “blue states”—while Republicans were unexcited about John McCain. This allowed him to fully utilize Howard Dean’s “Fifty State Strategy,” putting states into play that most would never dream could be competitive. But then McCain picked Sarah Palin, which galvanized his party’s right-wing base. Although McCain’s post-convention “bounce” has now evaporated (and economic woes indicate a Democratic victory in November), the damage has been done. Sarah Palin is a force of polarization—driving a wedge between “liberal America” and “conservative America,” and re-igniting our country’s culture wars. Beyond the excitement that Palin brought to the Bible Belt, she has also elicited a backlash from coastal liberals. If progressives want Obama to be the next President, they should not take the bait that this polarization has brought—or complain about “how stupid” American voters are. Better to contrast division with unity.

I’ll never forget a conversation I had in 2004 with a friend here in San Francisco—one month before the election. “I’m afraid George Bush is going to win,” she said nervously. “I just have no faith in middle America.” Bush’s victory—propelled by his party’s right-wing evangelical base—confirmed the disgust that many liberals have about national politics.

But how can insulting the intelligence of people who live in what we derisively call “fly-over country” be anything but counter-productive? San Franciscans and other “blue-state” liberals always have this inferiority complex that they somehow don’t represent America. But we’re Americans too, and wallowing in self-pity as Republicans wage a culture war doesn’t help win “swing-vote” independents who make or break a presidential candidate.

Which is exactly what the Republican playbook is about: polarize, divide and conquer to keep power by any means necessary. But Obama has always been the antithesis of that mentality. At his famous speech at the 2004 Democratic National Convention, he said: “there is not a liberal America and a conservative America—there is the United States of America.” Obama’s campaign message—which helped him win the primaries, and is now helping him win independent voters—is that we can do better than remain paralyzed by the culture wars that have dominated American discourse for 40 years.

Such a strategy was wildly successful for much of the campaign season—as McCain suffered a huge “enthusiasm gap.” With Howard Dean running the Democratic National Committee, Obama executed his “Fifty State Strategy”—putting resources that paid off dividends in unlikely places. It even looked like Obama could win Alaska or North Dakota. And while Georgia was always a long shot, the state’s large African-American population—coupled with ex-Congressman Bob Barr playing “spoiler” for McCain—convinced Obama to put resources there, hoping to score an unlikely victory.

Then, John McCain picked Sarah Palin as his running mate. Despite being phenomenally unqualified to be Vice President, it was a blatant political move: pander to the party’s right-wing base, and hope enough independent white women get excited about breaking the “ultimate glass ceiling.” For a while, it worked. Polls after the Republican Convention showed the race neck-and-neck, and Democrats panicked about losing yet another election.

For a stunning contrast, watch the 2004 Democratic Convention speech where Barack Obama spoke about unity—and compare it with Sarah Palin’s 2008 Republican Convention speech, where she fiercely goaded the right-wing into a frenzy against “community organizers.”

Now Palin’s stock is falling—because independent white women have learned more about her and aren’t impressed, and the economic climate has turned against Republicans. But observers are wrong when they read poll numbers and conclude it’s back to how things were before the Conventions. Now the right-wing evangelical base has one of their own on the ticket, and they are energized in states where they are strong to get out the vote. Expect more “red-meat” rhetoric about creationism, school prayer and abortion—and other wedge issues that inflame the culture war.

At the same time, these hot-button evangelical issues have stoked the contempt liberals have about so-called “fly-over country.” How many times in the last few weeks have you heard San Francisco Democrats lament (or make fun of) “stupid” red state voters? How many times does reacting to this rhetoric only make liberals look like the coastal elitists that Republicans always accuse them of being? Obama’s base supporters almost fell for this trap again—which only further divides Americans along the “blue vs. red” divide.

Obama is still favored to win, because independent voters in swing states like Nevada, Colorado, Virginia, New Mexico and Ohio are more likely to support him—especially in these tough economic times. But the immediate “Palin-effect” of this race is that Obama can no longer be competitive in states like Georgia, Alaska or North Dakota—states where the Democratic Party had chances to expand on Obama’s “unity” message, helping to build the party down the road. With the right-wing base ready to wage another “culture war,” the same old battle lines have been drawn once again.

The race will now come down to the “swing states,” where a few thousand votes can dramatically alter our country’s direction for the next four years. Palin’s legacy—regardless of the final outcome—is to bring us back to the politics of division and 50%-plus-one victories, and for Republicans that is their victory. Obama will still prevail in the end, but it won’t be pretty. And it could make it tougher for him to govern next year.