There is no shortage of hypotheses about what the tea party movement is. Some embrace it as a revival of traditional conservatism. Many insist it is ginned up by billionaire funders as a means to fight regulations. Others view it as arch-social conservative Republicans, motivated by divisive issues like abortion, gay rights or even racial angst.

But all these explanations are missing much of the story. Libertarian attitudes are fueling roughly half the tea party activists, according to our new Cato Institute survey. These libertarian tea partiers believe “the less government the better” and don’t see a role for government in promoting “traditional values.” This is a big reason why the movement has largely focused on economic matters, resisting attempts to add social issues to its agenda.

President Barack Obama and the Democrats may well have over-interpreted the 2008 election as a mandate for liberalism. Now Republicans could be in similar danger if they over-interpret potential midterm gains in the House and Senate as a mandate for social as well as fiscal conservatism. Republicans should focus on a unifying economic agenda, according to our data, to avoid antagonizing the libertarian half of the Tea Party.

Just under half, or 48 percent, of tea partiers at the recent Virginia Tea Party Convention held views that are more accurately described as libertarian — fiscally conservative, to be sure, but moderate to liberal on social and cultural issues.

Many of these activists, however, are unfamiliar with the word “libertarian.” Rather, 60 percent of the libertarian tea partiers label themselves as “independent” or “something else,” compared to 37 percent of tea party conservatives. The other half of our survey sample, roughly 51 percent, held traditional conservative views — agreeing on “the less government the better” but also believing that government should promote traditional values.

Many still mistake the tea party as one large group, sharing common interests, which our research shows is incorrect. Understanding the tea party’s two halves — libertarian and conservative — may help unravel the seemingly contradictory impulses of the group: If it is an independent movement, then why do tea party supporters plan to vote overwhelmingly Republican?

Tea party libertarians tend to be more independent and less loyal to the GOP than tea party conservatives. The conservative members identify themselves as 63 percent Republican, according to our data, and 30 percent independent. But tea party libertarians identify as 39 percent Republican and 44 percent independent. When asked whether the Republican or Democratic Party has the best ideas to fix government, 80 percent of tea party libertarians said “neither can be trusted,” compared to 64 percent of conservatives.

While 92 percent of tea party conservatives report voting for Sen. John McCain in 2008, only 75 percent of Tea Party libertarians supported him, with 16 percent backing third parties. Asked what political figure best exemplifies the tea party movement, libertarians are more likely to choose Ron Paul. Conservatives choose Glenn Beck or Sarah Palin.

Tea party libertarians are somewhat younger, better educated and almost twice as likely to “never” go to church than tea party conservatives. On the issues, tea party libertarians are less concerned than conservatives about the moral direction of the country, gay marriage, immigration, job outsourcing and abortion.

However, tea party libertarians and conservatives share economic concerns. Both groups are extremely concerned about cutting federal government spending, reducing the size of government and the recently passed health care reform.

Some might say that two Cato Institute analysts are likely to find libertarians everywhere. But our survey replicates a Politico/​Targetpoint survey from a tea party rally in April, which also revealed an even split between libertarians and conservatives.

This is reflected as well in a new national survey from The Washington Post/​Kaiser/​Harvard on the role of government. It found respondents who support or lean toward the tea party split on the social issues: 42 percent moderate-to-liberal, 57 percent conservative or very conservative.

Putting these tea party libertarians in historical context further clarifies this. In past elections, libertarians often voted 70 percent for Republican candidates. But during the Bush administration, the GOP expanded entitlements and spent taxpayer money faster than Democrats. Polls in 2004 and 2006 showed libertarian voters shifting to the Democrats. Their move may well have cost Republicans control of Congress.

In fact, libertarians were angry about President George W. Bush’s policies — and Washington in general — before most conservatives were. In 2004, 56 percent of libertarians were angry about Bush, according to American National Election Studies data, compared to 32 percent of conservatives.

Today, libertarians and conservatives are united in their anger — 79 percent of tea party libertarians are angry about Washington, compared to 74 percent of tea party conservatives. Libertarians may again have led the way.

Traditional conservatives often organized around church, gun clubs or the Christian Coalition, while libertarians were less likely to be an organized, visible force in politics. Now libertarians have the tea party — or at least half of it.