A perfectly normal looking couple come to sit opposite you on the train. They seem pleasant enough and you fall into conversation, but you soon note that the man is not making a lot of sense and foam is showing at the corners of his mouth. At every turn, he contradicts his partner or, more weirdly, himself, and you realise that inside he is seething with violent and paranoid fears. You conclude that this character is going to do serious harm to himself, and may hurt other passengers in the process, so you leave and find a seat in another carriage.

That's our experience of living with the American right – the Tea Party activists who have brought the world's largest economy to the brink of catastrophe to make one last stand against the Patient Protection and Affordable Care Act. The world is powerless to persuade or intervene and we are at the mercy of what seems truly irrational behaviour.

This is certainly some kind of high point in the Tea Party's mission to disrupt, but it cannot simply be written off as delinquency. The movement presents the symptoms of a prolonged infantile spasm, at the same time as a coherent belief that central government and especially Obamacare are inimical to the liberty of the individual and the freedom of individual states to determine their future.

Liberals will describe this as a failure of consensus politics that has been driven by the lowest suspicion and prejudice available in American society, manipulated by big business, pandered to by lax or demagogic media companies, such as Fox News, and ridden by ambitious politicians who promise a fantasy land that they cannot deliver.

That's mostly my view, yet I have to concede that it ignores the deep suspicion of centralised power in America that goes back to the founding fathers and is an essential part of national culture. The checks and balances designed by the authors of the constitution seem archaic in a world that demands swift executive action, but we shouldn't forget that even though Obamacare has been democratically scrutinised and passed by Congress, the restraints are being applied by the Tea Party or TPers – in the name of liberty.

There is still a minority – 18-20 – of Republicans in the Senate who oppose the government shutdown and recoil from a default, which would mean the government would stop paying its bills when it reaches its debt limit on or after 17 October, and so cause a greater international crisis than anything we have seen in the last five years. It's obviously suicidal, but, for the moment, Tea Party representatives, such as Ted Cruz, the junior Republican senator for Texas who made a 21-hour filibustering speech attacking everything about the White House except Mrs Obama's vegetable garden, are calling the shots.

But the strategy, if that is the word, is bound to fail, because President Obama cannot resile on the key reform of his administration and, at some point, the Tea Party has to swerve or risk the anger of the majority of the American people and so jeopardise the Republican party's chances at the next presidential election.

The movement has placed itself in a position where it cannot win and that is going to be very damaging to its Republican host, which has already been greatly distorted by the invasive Tper micro-organism. As the Economist points out, Republican members of Congress have become more fearful of being challenged by their own extremists than losing at a general election. "Many pander to extremists on their own side rather than forging sensible alliances with the other," says the magazine's leader.

A couple of weeks ago, writing about gun control in the US, I applied the ironic technique of treating America with the same condescension that America speaks about other nations. But those tropes would be pointless for the Tea Party, for there are few movements anywhere in the world that are so unrealistic or have such a startling lack of rigour. Satire and irony are useless when it comes to a movement that is pro-life on abortion but pro-death in the matter of executing people or the 32,000 yearly toll caused by privately owned firearms. Tea Party Republicans pepper their speeches with the words "freedom" and "liberty", but do nothing to oppose the government surveillance programmes that infringe the rights of all Americans. They rail against the power of big government, but never the malignancy of big business.

They are all over the map. Their policies are like the diet of high fructose corn syrup that Tpers often favour – appetising, temporarily satisfying but ultimately a health hazard.

We have our own political boobies, in Ukip and the Conservative party, (Jacob Rees-Mogg applauded the US government shutdown) but we are rarely exposed to the dazzling fanaticism of a man such as Cruz. He was elected last November but has already become a national figure and is being touted as a possible presidential candidate in 2016. Princeton and Harvard educated, with a Cuban father, he looks quite a bit like a young version of Senator Joe McCarthy. And indeed, shortly after arriving in Washington, his prosecutorial line of questioning of Chuck Hagel, Obama's nominee for defence secretary, with its references to possible ties to foreign enemies, reminded people of McCarthy. "Are you or have you ever been…"

I recommend his filmed interviews, especially with Evan Smith of the Texas Tribune, because you will not see a more polished zealot. This is a man who agreed that social security was a Ponzi scheme on the grounds that it paid investors from their own money or the money invested by others. He regards many of his colleagues as "squishy Republicans" and repeats this refrain: "The federal government is engaged on a war on jobs and what is at stake is individual liberty and the constitution", which makes absolutely no sense, given the hundreds of thousands of government employees now on unpaid leave because of the shutdown.

If you found yourself on a train with Cruz, you would be struck by his intelligence and confident manner, and initially you might buy his line that the constitution needs to be redrafted to beef up the 9th and 10th amendments, which he says would enhance individual liberties and the states' powers. But very soon you'd see none of it adds up and that his suspicion of government is far greater than his love of liberty.

The constitution may need to be rewritten, but only to give the executive the power to govern the modern American state and bring order to the country's finances. For in all this no one mentions the elephantine figure in the room – America's debt, last estimated to be $16,699tn.