Perhaps my biggest frustration with the U.S. news media (and yes, I am a card-carrying member) is that we permit the two parties to decide what is “left” and what is “right.” The way it works, roughly, is that anything Democrats support becomes “left,” and everything Republicans support becomes “right.”

There are good reasons for this. It isn’t the media’s job to police political ideologies, and it wouldn’t be a good idea for us to try. But that leaves ordinary voters in a bit of a tough spot.

The reality is that most Americans aren’t policy wonks. They don’t sit down with think-tank papers or economic studies and puzzle over whether it’s better to address the free-rider problem in health care through automatic enrollment or the individual mandate. Instead, they outsource those questions to the political actors they trust.

Unfortunately, those political actors aren’t worthy of their trust. They’re trying to win elections, not points for intellectual consistency. So the voters who trust them get taken for a ride.

Consider the partywide flips and flops of just the past few years:

-- Supporting a temporary, deficit-financed payroll-tax cut as a stimulus measure in 2009, as Republican Senator John McCain and every one of his colleagues did, put you on the right. Supporting a temporary, deficit-financed payroll tax-cut in late 2011 put you on the left. Supporting it in early 2012 could have put you in either party.

-- Supporting an individual mandate as a way to solve the health-care system’s free-rider problem between 1991 and 2007 put you on the right. Doing so after 2010 put you on the left.

-- Supporting a system in which total carbon emissions would be capped and permits traded as a way of moving toward clean energy using the power of market pricing could have put you on either the left or right between 2000 and 2008. After 2009, it put you squarely on the left.

-- Caring about short-term deficits between 2001 and 2008 put you on the left. Caring about them between 2008 and 2012 put you on the right.

-- Favoring an expansive view of executive authority between 2001 and 2008 put you on the right. Doing so since 2009 has, in most cases, put you on the left.

-- Supporting large cuts to Medicare in the context of universal health-care reform puts you on the left, as every Democrat who voted for the Affordable Care Act found out during the 2010 election. Supporting cuts in the context of deficit reduction puts you on the right, as Republicans found out in the 1990s, and then again after voting for Representative Paul Ryan’s proposed budget in 2011.

-- Decrying the filibuster and considering drastic changes to the Senate rulebook to curb it between 2001 and 2008 put you on the right, particularly if you were exercised over judicial nominations. Since 2009, decrying the filibuster and considering reforms to curb it has put you on the left.

-- Favoring a negative tax rate for the poorest Americans between 2001 and 2008 could have put you on the right or the left. In recent years, it has put you on the left.

I don’t particularly mind flip-flops. Consistency is an overrated virtue. But honesty isn’t. In many of these cases, the parties changed policy when it was politically convenient to do so, not when conditions changed and new information came to light.

There are exceptions, of course. It’s reasonable to worry about short-term deficits during an economic expansion and consider them necessary during a recession. That’s Economics 101.

But nothing happened to explain the change from 2006, when the individual mandate was a Republican policy in good standing, to 2010, when every Senate Republican, including those who had previously supported it, agreed it was an unconstitutional assault on liberty. Nothing, that is, but the Democrats’ adopting the policy in their health-care reform bill.

Flips and flops like these make the labels “left” and “right” meaningless as a descriptor of anything save partisanship over any extended period of time. I could tell you about a politician who supported deficit-financed stimulus policies and cap-and-trade, and I could be describing McCain. Or Newt Gingrich. And I could tell you about another politician who opposed an individual mandate, and who fought deficits, expansive views of executive authority and efforts to reform the filibuster, and be describing Senator Barack Obama.

Parties -- particularly when they’re in the minority -- care more about power than policy. Perhaps there’s nothing much to be done about this. And as I said, it isn’t clear that the media, or anyone else, should try. But it puts the lie to the narrative that America is really riven by grand ideological disagreements. America is deeply divided on the question of which party should be in power at any given moment. Much of the polarization over policy is driven by that question, not the other way around.

But the voters who trust the parties don’t know that, and they tend to take on faith the idea that their representatives are fighting for some relatively consistent agenda.

(Ezra Klein is a Bloomberg View columnist. The opinions expressed are his own.)

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To contact the writer of this article: Ezra Klein in Washington at wonkbook@gmail.com.

To contact the editor responsible for this article: Timothy Lavin at tlavin1@bloomberg.net.