Will there be blood? • The question sounds farfetched. But consider the extreme hatred that seems to be driving American politics right now. Case in point: A judge in Texas warned that a "civil war" was possible if President Barack Obama is re-elected. • Partisan hatred is nothing new. We had plenty of Bill Clinton-haters in the 1990s and George W. Bush-haters in the 2000s. Clinton-haters resented Clinton because of his values. Obama-haters, however, go one step beyond. They assert Obama's not a real American. That's what the birther movement is all about.

Some delegates at the Republican National Convention in Tampa last week were wearing T-shirts saying, "I am pro-American, anti-Obama." That defines Obama as ... anti-American.

Look at the intemperate language being used by Obama's opponents. "We need to prosecute the president on what he promised and what he delivered," Republican Party chairman Reince Priebus said to Charlie Rose on CBS Wednesday.

"Prosecute?" Rose interjected.

Priebus persisted, "We need to prosecute the president."

George Packer reports in the New Yorker on a rally of Tea Party Patriots at the Republican convention. "Some speakers were openly accusing Obama of working for the enemy," Packer writes. What drove the GOP convention, in Packer's view, was "hatred — hatred of Barack Obama and hatred of what the people here believe he's done to their country."

It was at a Republican National Convention nearly 50 years ago that Sen. Barry Goldwater said, "Extremism in the defense of liberty is no vice." That view appears to have really caught on.

After the Supreme Court upheld the Affordable Care Act this summer, a movement to nullify the new law emerged in conservative states like Oklahoma. Nullification was a doctrine promoted by Southern states before the Civil War.

If the health care law becomes fully effective in 2014, some militant could hole up in a cabin in northern Michigan with a stockpile of guns and dare the federal government to come after him for refusing to purchase health insurance.

Sound farfetched? Here's what vice presidential nominee Paul Ryan had to say about "Obamacare" when he addressed the convention Wednesday: "Obamacare comes to more than 2,000 pages of rules, mandates, taxes, fees and fines that have no place in a free country." Isn't one justified in resisting something that "has no place in a free country"?

We have seen what extreme hatred of government can lead to: Oklahoma City, 1995 — 168 people killed, nearly 700 injured.

A student asked me, "Is this the most divided we have ever been as a country?" I reminded the student that we did, once, have a civil war. Three-quarters of a million Americans were killed. But I acknowledged that this is probably the most divided we've been since that dreadful time.

The polls back that up.

The Gallup poll has a simple index to measure partisan polarization: the difference between the job ratings presidents get from members of their own party and from members of the opposition party. For the six presidents before Ronald Reagan (Dwight D. Eisenhower through Jimmy Carter), the difference averaged 34 points. From Reagan through George W. Bush, the difference between Republicans and Democrats jumped to 55 points.

And now? In polls taken over the past month, Obama averages 84 percent support from Democrats and 9 percent from Republicans. A 75-point gap!

In 1998, according to a Washington Post-Kaiser Family Foundation poll, 24 percent of Republicans felt strongly that "government controls too much of our daily lives." Now 63 percent feel that way. The Post reports, "The number of Democrats strongly disagreeing with the assertion doubled."

Partisan animosity has increased on both sides. But among Republicans, more so. In the Post-Kaiser poll, most Democrats endorsed the idea that Democrats should try to cooperate across party lines "even if it means compromising on important issues." Most Republicans said the GOP should stick with its positions "even if it means a lack of cooperation with Democrats."

Yes, people on the left sometimes say extreme things. A news director lost his job last week for saying that Mitt and Ann Romney were "happy to have a party with black people drowning" when Hurricane Isaac hit. Chuck Thompson has just written a book called Better Off Without 'em: A Northern Manifesto for Southern Secession. He isn't joking.

The theme of the Republican convention was "We built it." It was an orchestrated rebuke to Obama's remark that "You didn't build that." It's also a way of making the point that Obama doesn't understand America or free enterprise. GOP presidential nominee Mitt Romney said that Obama has "tried to substitute government for free people." Sen. Rand Paul, R-Ky., said, "Anyone who so fundamentally misunderstands American greatness is uniquely unqualified to lead this great nation."

Meanwhile, Mike Huckabee called attention to "the vast difference between the liberty-limiting, radical left-wing, anti-business, reckless-spending, tax-hiking party of Barack Obama, Harry Reid and Nancy Pelosi, versus an energized America that knows we can do better." Not Democrats versus Republicans. Democrats versus America.

Defining Obama as anti-American can be dangerous. It eases the pathway toward an incitement to resistance, and even violence.

It was once said that parties of the left and right in France didn't just dream of defeating each other. They dreamed of annihilating each other. That kind of extreme partisanship has been alien to the United States.

Until now.

Bill Schneider is professor of public and international affairs at George Mason University and a resident scholar at Third Way.

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