For more than a year, the United States has gone through a contentious and divisive debate over health reform, but in the past fortnight these divisions turned genuinely nasty.

In the wake of vilification, threats and vandalism, some leaders within the Republican Party and the activist Tea Party movement have stepped forward to condemn the violence and harassment. But the problem is that the seeds of this dangerous and volatile reaction to health care's passage were sown months ago. However they might try to defuse the situation now, it seems that this aggression against the government was, to some extent, stoked by the message conservative leaders used in fighting Barack Obama's push for health reform.

The ugliness began in the days leading up to the votes on health care legislation, when anti-reform protesters yelled racist and homophobic slurs at Democratic lawmakers and one Democratic Congressman was allegedly spat on. Democratic Party politicians have received death threats and had their offices vandalised. In the most dangerous act of hostility so far, the brother of Virginia Representative Tom Perriello had the propane gas line to his house cut after Tea Party activists posted his address online and encouraged people to "drop by," in the mistaken belief it was the Congressman's home.

These acts aren't orchestrated or organised, but at this point they are far from isolated - which means that it is important to consider where the increase in violent and threatening behaviour might come from. It's easy to dismiss these as the acts of disturbed people who have channelled their anger at the health reform legislation into unacceptable responses. But what type of person might be prone to such extreme reactions to the passage of a law, and what factors might make someone more likely to do so? I suspect that a plausible answer to those questions comes from the evidence about right-wing authoritarianism, and from the approach American conservative leaders have taken to motivating authoritarian followers.

Our understanding of authoritarian followers stems from the work of Dr Bob Altemeyer at the University of Manitoba in Canada, although his findings have been replicated and extended by researchers around the world. Altemeyer found that people high in authoritarianism display three tendencies: to submit to the people they see as legitimate authorities in society (authoritarian submission), to believe that everyone should follow the customs and traditions of society (conventionalism), and to be aggressive toward anyone defined as an opponent or transgressor by the authorities (authoritarian aggression).

Not all conservatives are authoritarians, and authoritarianism is not exclusive to conservative politics. But in recent years the Republican Party has taken a direction that increasingly appeals to an authoritarian base. With their emphasis on a single set of dominant values, both neoconservatism and the religious right seem consistent with the way authoritarians view the world. Former Nixon lawyer John Dean's book, Conservatives Without Conscience, drew on Altemeyer's work to highlight the rise of authoritarian control in the Republican Party.

Since the 2008 election, the Democratic Party has controlled the White House and both houses of Congress. How has the conservative movement retained and motivated the authoritarian followers in their base? By attacking not just the appropriateness of Obama's policies but the legitimacy of his government. At the furthest extreme has been the "birther" movement, which claims Obama was born in Kenya and is ineligible to be President. But as early as the Presidential campaign Obama has been targeted by accusations that imply his rise to power has been illegitimate, such as the attempts to paint him as "palling around with terrorists" and being aided by voter registration fraud, or that he cannot represent America's values because of his mixed heritage and the idea that he might be a Muslim. His approach to government and policy has been repeatedly likened to Hitler, Marxism, fascism, and almost any other ideology or regime that has a negative connotation in the United States.

In a nation of 300 million, it's almost inevitable that conspiracy theories and extreme views are going to exist about any leader. What matters is that these attacks on Obama's legitimacy haven't just come from the fringe of the conservative movement - they have been put forward, endorsed and encouraged by conservative leaders. High-rating personalities on the media outlets most trusted by conservatives, such as FOX News' Glenn Beck and Sean Hannity and talk radio host Rush Limbaugh, have stated and fostered views that Obama is a socialist or a fascist, that his policies are unconstitutional and undermine American sovereignty, and that his actions are similar to Hitler's.

And Republican politicians have aligned themselves with these messages. A few examples among many: When asked last December about the "birther" movement's questions about Barack Obama's birth certificate, Sarah Palin said, "I think the public rightfully is still making it an issue. I don't have a problem with that." At a Tea Party rally last April, Texas's Governor Rick Perry skirted very close to advocating secession. Several Republican Representatives, including John Linder and Paul Broun of Georgia and Steve King of Iowa, have compared Obama's government to Hitler's Germany.

It's hardly surprising then that many conservatives don't just dispute Obama's policies, but feel his Presidency endangers America's integrity. Exactly how many is hard to estimate - several polls have tried, most recently a Harris poll and before that a Research2000 poll. Each has had its flaws and likely overestimates the true numbers, but it seems safe to conclude that some conservatives believe Obama is not a native-born citizen, stole the election with ACORN's help, is a socialist and/or fascist, and is a Muslim who doesn't share their values.

For the authoritarian followers who have heeded this message, submission to authority might well give way to aggression against what are seen as illegitimate attempts at control. What's more, research has shown that a perceived threat enhances the effects of authoritarianism - which means that when leaders describe the passage of health reform as "Armageddon" that will "ruin our country", as House Minority Leader John Boehner did, we might expect that the tension and aggression will be heightened.

Australian politics might have its share of character attacks and appeals to emotion, but the conflict of ideas remains an important part of our discourse. Our debate over emissions trading was divisive, both within and across party lines, but it was largely based on principles and policies and certainly did not see widespread aggression or threats. In this election year, we can expect that the debate will remain civil and focused on the issues. Given the current tensions in America and their roots in the way authoritarian followers are exploited, we can consider ourselves a lucky country in that regard.

David Mallard is a Senior Lecturer in Psychology at Charles Sturt University in Bathurst.