In the classic teen movie Animal House there comes a moment when the ne'er-do-well students of the Delta fraternity finally realise their pranks have gone too far. Faced with expulsion from university, the most violent, antisocial drunkard of the group, Bluto Blutarsky (John Belushi), gives one last rousing, rambling speech to his crestfallen comrades. "Nothing is over until we decide it is," he yells. "Was it over when the Germans bombed Pearl Harbor? Hell, no!"

The other students look on confused. Bluto leads a charge but nobody follows. However, they soon fall in line after the fraternity's leader, the far more respectable, presentable, all-round-cad, Otter (Tim Matheson), backs Bluto's call to arms against the university authorities. "Bluto's right," he says. "Psychotic, but absolutely right. We gotta take these bastards … I think we have to go all out. I think that this situation absolutely requires a really futile and stupid gesture be done on somebody's part."

The Republican party, in particular, and American conservatism in general, have taken to operating in a similar manner to the Delta fraternity – increasingly reckless, anarchic and strident. Faced with defeat they respond with desperation. Only where the Deltas were motivated by ribaldry, conservatives are driven by rage.

On the one hand there are the Blutos – characterised by their contempt for even the most basic facts. Their assertions are often not only verifiably false but patently ridiculous. The very people who claim that Obama is a Muslim were the ones who fumed about his relationship with Reverend Jeremiah Wright, his pastor in Chicago. Muslims don't have pastors. Last year the Investor's Business Daily claimed that if the renowned scientist Stephen Hawking were British he would be dead: Hawking is British and alive.

These falsehoods are not limited to the fringes. A recent Harris poll reveals that a majority of Republicans believe Obama is a Muslim and a socialist who "wants to turn over the sovereignty of the United States to a one-world government". A Daily Kos poll in January showed that about two-thirds of Republicans either believe or are not sure that Obama is "a racist who hates white people", and more than half believe or are not sure that he was not born in the US and that he wants the terrorists to win.

So long as these people breathe the ever more fetid air of their own ecosystem – oxygen provided by Fox News – then these contradictions are of little concern or consequence to them. Cognitive dissonance is not the exception but the rule. But there is menace in this madness. A few weeks ago, shortly before the passing of the healthcare vote, conservative blogger Solomon Forell tweeted: "We'll surely get over a bullet 2 Barack Obama's head!" He added: "The Next American with a Clear Shot should drop Obama like a bad habit. 4get Blacks or his claim to be Black. Turn on Barack Obama." Last week a man was detained for issuing death threats to Democratic senator Patty Murray. Speaking in Phoenix on a Tea Party tour, Joe the Plumber, recently spelt out his plan for dealing with illegal immigration: "Put a fence in and start shooting."

So much for the Blutos. Far from reining them in, the Republican leadership increasingly reflects their excesses. Absent any legislative agenda or coherent ideological approach, they have spent the last two years crafting "a really futile and stupid gesture … on somebody's part" that Otter would be proud of. Small government is a legitimate philosophical and political position. But in the hands of people who voted to bloat the deficit and unleash a huge state-grab of civil liberties, it is shorn of credibility. It isn't government they don't like; it's Democrats in government.

So congressmen scream "liar" at the president and "baby killer" at their colleagues; senators repeat myths about death panels; and legislators stoke up crowds from the balconies during the healthcare debate. On Friday at the Southern Republican Leadership conference, Sarah Palin repeated her slogan: "Don't Retreat, Reload." This time she insisted it was "not a call for violence". The fact she would have to make that explicit tells us something about how dire things have become.

The potential for this kind of rhetoric to produce an unthinkable calamity should not be underestimated. Last year a Homeland Security report, Rightwing Extremism: Current Economic and Political Climate Fuelling Resurgence in Radicalisation and Recruitment, concluded: "The economic downturn and the election of the first African-American president present unique drivers for rightwing radicalisation and recruitment."

Such people are on the fringes. But those fringes are growing. In any case, it only takes one angry person with a gun to make the difference. If such a person were to emerge, they would not be acting alone. Thousands of others, from the blogosphere to Congress, have colluded in creating an alternative reality that would explain, if not justify, their actions. After all, if Obama truly were a foreign-born, white-hating, terrorist sympathiser who has usurped the presidency, drastic action would make sense.

Meanwhile, the brazen disregard for basic facts goes all the way to the top. The 2008 presidential contender John McCain recently insisted he never considered himself a "maverick", even though one of his books is subtitled The Education of an American Maverick, and he called himself "the original maverick" in campaign ads. It used to be assumed this was the tail wagging the dog. But by increments it is turning into an entirely new breed of dog. Establishment Republicans are not running away from Palin's wing of the party but towards it. McCain needed her endorsement to fight off a Tea Party challenge in Arizona.

This trend is not new. Ever since the Republican election rallies of 2008, where Obama's name provoked screams of "traitor" and "terrorist", this dialectic between leadership and base, margins and mainstream, populist reaction and legislative response, has been all too evident. Far from subsiding, the contradictions have sharpened.

Whereas in 2008 McCain grabbed the microphone from an audience member's hand and corrected her after she said she didn't trust Obama "because he's an Arab", the metaphorical mic has now been returned to her and she has been ushered to centre stage.

Having pitted fear against hope and lost, the Republican leadership has come up with no better alternative than to keep doubling down on fear. None of this puts food on Blutos' tables, but it does keep them angry. For those who peddle in rumour and angst, this is a lucrative market indeed. In a world where facts don't matter, their fears can never truly be assuaged.

Quite how reality will intrude into this parallel universe is as of yet unclear. But it will. Now that healthcare legislation has been passed, people will see that the state does not kill their grandmothers and most Republican voters will see their healthcare costs fall. This week there will be an anti-tax rally – most of the protesters on it will actually see their taxes lowered by the Obama administration.

And how would the Republican party explain to most of its supporters that while their living standards stagnated or declined under George Bush they are set to improve under Obama? As Otter explained to one of the fraternity after trashing his brother's car: "You fucked up ... you trusted us!"

• This article was amended on 12 April 2010. The original version spelled Stephen Hawking's name as "Steven". This has now been corrected