[Beinart is associate professor of journalism and political science at the City University of New York and a senior fellow at the New America Foundation. His book The Icarus Syndrome: A History of American Hubris will be published by Harper in June.]

How polarized is America today? Not all that polarized by historical standards. In 1856, a South Carolina Congressman beat a Massachusetts Senator half to death with his cane in the Senate chamber — and received dozens of new canes from appreciative fans. In 1905, Idaho miners bombed the house of a former governor who had tried to break their union. In 1965, an anti–Vietnam War activist stationed himself outside the office of the Secretary of Defense and, holding his year-old daughter in his arms, set himself on fire. (She lived; he did not.) By that measure, a Rush Limbaugh rant isn't particularly divisive. Americans may yell at one another about politics, but we mostly leave our guns and bombs at home, which is an improvement. (See 10 embarrassing things that didn't stop Americans from getting elected.)

What really defines our political era, as Ronald Brownstein notes in his book The Second Civil War, is not the polarization of Americans but the polarization of American government. In the country at large, the disputes are real but manageable. But in Washington, crossing party lines to resolve them has become excruciatingly rare....

The vicious circle has its roots in the great sorting out of American politics that has occurred over the past 40 years. In the middle of the 20th century, America's two major parties were Whitmanesque: they contradicted themselves; they contained multitudes. As late as 1969, the historian Richard Hofstadter declared that the Democratic and Republican parties were each "a compound, a hodgepodge, of various and conflicting interests."

But in the 1960s and '70s, as liberal Northern Democrats rallied behind civil rights, abortion rights, environmentalism and a more dovish foreign policy, conservative Southern Democrats began drifting into the GOP. And as the Republican Party shifted rightward, its Northern liberals became Democrats. Whereas many members of Congress had once been cross-pressured — forced to balance the demands of a more liberal party and a more conservative region, or vice versa — now party, region and ideology were increasingly aligned. Washington politics became less a game of Rubik's Cube and more a game of shirts vs. skins.

The first shirts-and-skins President was Ronald Reagan, the first truly conservative Republican elected in 50 years. But it was only after Reagan and his GOP successor, George H.W. Bush, left office that congressional Republicans realized they could use political polarization to stymie government — and use government failure to win elections. And with that realization, vicious-circle politics started to become an art form....

In the Clinton years, Senate Republicans began a kind of permanent filibuster. "Whereas the filibusters of the past were mainly the weapon of last resort," scholars Catherine Fisk and Erwin Chemerinsky noted in 1997, "now filibusters are a part of daily life." For a while, the remaining GOP moderates cried foul and joined with Democrats to break filibusters on things like campaign finance and voter registration. But in doing so, the moderates helped doom themselves. After moderates broke a 1993 filibuster on campaign finance, GOP conservatives publicly accused them of "stabbing us in the back." Their pictures were taken off the wall at the offices of the Republican Senate campaign committee. "What do these so-called moderates have in common?" conservative bigwig Grover Norquist would later declare. "They're 70 years old. They're not running again. They're gonna be dead soon. So while they're annoying, within the Republican Party our problems are dying."...

All this, it turns out, was a mere warm-up for the Obama years. On the surface, it appeared that Obama took office in a stronger position than Clinton had, since Democrats boasted more seats in the Senate. But in their jubilation, Democrats forgot something crucial: vicious-circle politics thrives on polarization. As the GOP caucus in the Senate shrank, it also hardened. Early on, the White House managed to persuade three Republicans to break a filibuster of its stimulus plan. But one of those Republicans, Pennsylvania Senator Arlen Specter — under assault for his vote and facing a right-wing primary challenge — switched parties. That meant that of the six Senate Republicans with the most moderate voting records in 2007, only two were still in the Senate, and in the party, by '09. The Wednesday lunch club had ceased to exist. And the fewer Republican moderates there were, the more dangerous it was for any of them to cut deals across the aisle....

In recent years, Republicans have played this style of politics better than Democrats. Winning elections by making government look foolish is a more natural strategy for the antigovernment party. But there's no guarantee Democrats won't one day try something similar. Were a Republican President and Congress to make a genuine effort to rein in entitlement spending, Democrats might act in much the same way McConnell and company are acting now. At its core, vicious-circle politics isn't an assault on liberal solutions to hard problems; it's an assault on any solutions to hard problems. It's no surprise that Democrats couldn't successfully filibuster George W. Bush's tax cuts and Republicans couldn't successfully filibuster Obama's stimulus spending. When you're handing out goodies, it's much harder for opponents to gum up the process. As Vanderbilt University's Marc Hetherington has argued, trust in government matters most when government is asking people to make sacrifices. It's when the pain is temporary but the benefits are long-term that people most need to believe that government is something other than stupid and selfish. Which is exactly what they don't believe today.

Is there a way out? In theory, if the Democrats won so overwhelmingly that they controlled nearly 70 seats in the Senate, as they did when Franklin Roosevelt secured passage of Social Security and when Lyndon Johnson got Medicare through, they could simply steamroll the GOP. But America in 2010, unlike America in 1935 or '65, is closely divided between the two parties. Although bipartisanship is not an end in and of itself, the reality remains that today, and for the foreseeable future, neither party can do big, controversial things without help from the other....