American politics has become like a big square dance. When the music stops after an election, people switch to the other side on a number of issues, depending on whether their party remains in power.

That was pretty clear this week, when polls revealed more Democrats than Republicans support tracking of phone traffic by the National Security Agency — the exact opposite of where things stood under President George W. Bush.

A Washington Post-Pew Research Center poll released Monday showed that 64 percent of Democrats support such efforts, up from just 36 percent in 2006. Republican support, meanwhile, had dropped from 75 percent to 52 percent.

It's not just a question of whether you trust the current president to carry out data mining in a way that targets terrorists and not innocent Americans. Partisans hold malleable positions in a number of areas — foreign policy, the economy and even presidential appointees who continue to serve under a new administration.

"People change their views depending on which party is in power, and not based on objective conditions on the ground," says George Washington University political scientist John Sides.

My President, Right Or Wrong

It's not surprising that partisans are more willing to give one of their own a break, particularly when it comes to matters like scandals.

But the president — any president — has become like the New York Yankees. You either love him and root for his success, or you hate him.

Political scientists talk about a "perceptual screen" through which many voters view the world, tending to support certain policy stances based on where their party stands. Studies over the years have consistently shown that partisans tend to have a rosier view of the economy if someone they support is in the White House.

"Democrats support [military] interventions where Democratic presidents lead them," says James Stimson, a political scientist at the University of North Carolina. "Republicans support them when Republican presidents lead."

This isn't just blind faith. Most people don't spend their time reading position papers, so they look to their party's leaders for cues. If I'm with them on tax cuts and education, the thinking goes, I'll probably like their approach to immigration.

That's an increasingly safe bet in an era where the parties are almost perfectly sorted ideologically. There are few conservative Democrats left, certainly compared with 50 years ago, and practically no liberal Republicans.

So people can feel pretty secure that their party's position on a given issue is not going to be far out of line with how they think on other issues.

"Especially on a new issue, people are not very informed about the details of the policy, so they tend to accept the position of the political elites they trust, on the assumption they share the same interests," says Sunshine Hillygus, a political scientist at Duke.

An Important Identity

People aren't willing to flip-flop on every issue. Most people hold firm views on matters such as abortion and gun rights that won't change with new occupants in the White House or the speaker's chair.

But because opinion within parties tends to be so uniform — and gets reinforced by supportive media and social media circles — sometimes people's opinions do shift so that they line up better with their partisan brethren.

That may be the case, for instance, with gay marriage, support for which has become almost an article of faith among Democrats. A Fox News poll released Thursday found that 65 percent of Democrats support gay marriage, while 69 percent of Republicans oppose it.

Although many people like to describe themselves as independent, partisanship has become an important aspect of identity. Some are more loyal to their partisan leanings than their own church, says University of Notre Dame political scientist David Campbell.

"Our findings indicate that for many but not all Americans, when they're faced with this choice between their politics and religion, they hold fast to their politics and switch religion, or more often switch out of their religion," he says.

A recent Stanford University study found that people are more likely to have hostile feelings toward people of the other party than members of another race.

"People are more likely to see their party as in the right, no matter what, and the other party as wrong," says Shanto Iyengar, the Stanford study's lead author. "People get more upset if they are asked to contemplate the prospect of their son or daughter marrying outside the party than outside their religion."

Hating The Other Guy

Indeed, over the past 50 years, the percentage of people who said they would disapprove if their children married someone from the other party has spiked from 5 percent to 40 percent.

This is the flip side of tending to support the position of your own party: Many people today not only disagree with but despise the other party and its adherents.

Republican opposition to policies President Obama has proposed has been a hallmark of his entire administration. When Bush was in office, conversely, Democrats made no secret of their disdain or even hatred of him.

Voters have an intuitive sense this is going on. How many times over the past four years have you heard the phrase, "Imagine the outrage if Bush had done X?"

"The other side is not just your opponent, but bad and evil," says Lara Brown, an independent political analyst. "Everyone flips positions based on who's in power."

All this makes it more difficult to achieve lasting consensus. If politics is a matter of partisan loyalty and personality, it's difficult to convince the broad majority of the country that an idea is right, no matter what.

"When issues were uncoupled from parties, one could make an appeal on the merits," says Jack Pitney, a government professor at Claremont McKenna College. "But to the extent issues are associated with the party, you win by mobilizing the party."

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