Let me tell you what it feels like in right-wing Washington: tense. I’m not sure one word captures it, so let’s add two more: tense, baffled and spooked. Don’t mention the T-word. But no matter how many times members of Congress, staffers and think-tankers repeat this, every conversation swivels back to Donald Trump.

In Washington, they are insistent: Trump will never get the Republican nomination. But in the past week, which I have spent among conservatives in the American capital, I have heard this mantra shift from an assertion into a prayer. Please, God, stop the Donald.

Why is this happening? Every week for months, the serious set, the pen-in-pocket law-school grad set, have solemnly sworn that this is the week that Trump is peaking. Now, they are scrabbling for answers. Some explain the Trump effect with psychology: he is playing the emotions of American resentment like a flute. America’s old optimism, where everyone’s a winner, has since the financial crisis been replaced with America’s new pessimism, where only 25 per cent feel “their side” is winning and 64 per cent feel like “their side” is a bunch of losers.

Some free-marketeers explain the T-word in sociology: though you would never believe it judging by the faces in the corridors of power, this country is losing its white majority and its middle class. In 1980, more than half of US counties were more than 98 per cent white. Today, fewer than 5 per cent are. In 1980, 83 per cent of Americans were white; now, it’s only 63 per cent, and majority status is set to vanish around 2042. This year, the American middle class shrank to less than 50 per cent of the population, down from more than 60 per cent in 1970.

The ten best conspiracy theories Show all 10 1 /10 The ten best conspiracy theories The ten best conspiracy theories Apollo Moon Landing The Moon landing conspiracy theories claim that some or all elements of the Apollo program and the associated Moon landings were staged by NASA with the aid of other organisations Getty Images The ten best conspiracy theories 9/11 Pentagon conspiracy There's a theory that no plane actually hit the Pentagon on September 11 and that the explosion (pictured) was actually caused by a missile fired from inside it by the Americans. Theorists claim that no wreckage from the American Airlines Boeing 747 was actually found at the scene and that first accounts of the explosion were later doctored by the government. Other allegedly tell-tale signs, such as several windows surviving the crash intact, indicate that the blast was smaller than you’d expect from an aeroplane crashing in to a building Getty Images The ten best conspiracy theories Shakespeare is “Sheik Zubair” Some claim that William Shakespeare is actually Sheikh Zubair from Basra, Iraq. Others claim he was actually Francis Bacon, Christopher Marlowe, William Stanley and the list goes on. The Bard's connection to Iraq, it is claimed, is evidenced by a resemblance in his work to the teachings of the Islamic Sufi sect: "All the historical data and even the time-line conclusively proves that Sheikh Zubair was an Iraqi poet and author of plays from Basra," one Independent blogger recently claimed Getty Images The ten best conspiracy theories “Free energy” suppression Some claim that advanced energy technologies are being suppressed by groups profiting from oil and gas production. Claimants say that the phenomena of "free energy" has derived from impressive discoveries in superconductivity of electricity which violates our current understanding of science and would make energy easier to produce and more efficient. Access to this energy is being restricted by the controllers of the current industry, and possible links to the New World Order have been suggested Getty Images The ten best conspiracy theories The Bermuda Triangle A number of aircraft and ships are alleged to have gone missing in mysterious circumstances in the Bermuda Triangle, or Devil's Triangle. Strange goings on and supernatural activity has been reported since the 1950s. Recent aircraft disappearances in the area include: a Puerto Rican owned aircraft carrying 12 people that went missing in December last year; and a Piper type aircraft on a medical transport run which was lost from the radar in April 2007 The ten best conspiracy theories New World Order Theories abound that the world's power and financial systems are actually controlled by occult secret societies including the Bilderberg group and the Freemasons. This theory seeks to expose collusion between businessmen and politicians in these societies promoting its secret agendas. Theorists claim that there are many "signs" confirming such claims, including Masonic symbols on buildings, and pagan symbols such as pentagrams worked into planning regulations in New York Getty Images The ten best conspiracy theories Tin foil hats Some believe that wearing a tin foil hat will shield the brain against mind control, mind reading and electromagnetic fields.Typically made from the aluminium foil most of us use to wrap sandwiches, the protective powers of the tin foil hat have reached such heights of fame that cyber versions are now available in the online universe of the game World of Warcraft. They come in all shapes and sizes and are totally customisable Reuters The ten best conspiracy theories Paul is dead There is an urban legend alleging that Paul McCartney of The Beatles died in 1966 and was replaced by a look-alike and sound-alike. Theorists say that clues have been planted in Beatles' lyrics ever since, including some "mumbling" by John Lennon recorded between the songs I'm So Tired and the next song Blackbird, which when played backwards allegedly sounds like 'Paul is a dead man. Miss him.' He was supposedly replaced by William Campbell- the winner of a look-alike contest Getty Images The ten best conspiracy theories Princess Diana's death Some believe that the death of Prince Charles' ex-wife in a Paris car crash 12 years ago was a murder plot by the Royal family to prevent her from marrying again. When Diana, her boyfriend Dodi Fayez and their driver were killed in 1997 both Fayez's father Mohamed al Fayed and Diana's former butler Paul Burrell added fuel to the claim that she was murdered. Theories that she had been pregnant and letters claiming Charles was plotting her murder were published posthumously Getty Images The ten best conspiracy theories The Roswell cover up Many believe that the US military covered up the crash of an alien spacecraft in Roswell, New Mexico, on July 8, 1947 by claiming that the "flying disc" it recovered was a weather balloon Getty Images

Other right-wingers blame technology. With the breakdown of old media, there has been a breakdown of old editorial, too. Many Americans now receive their daily news through Facebook; news delivered in a bubble, echoing with the posts of those who agree with them.

Welcome to “Trumpland”. Things are different here. For a start, Barack Obama is a Muslim, born in Kenya, and schemes a plot against America. Trump was one of the first “Birthers” – the name given to agitators who promote the conspiracy theory that Barack Obama was not born in America, and is thus an impostor-fraudster, a constitutional illegality who should immediately stand down as President. He is, shouts Donald, the commander-in-chief of a country in which crowds of Muslims cheered as the Twin Towers fell on 9/11. Trump imagined it all. His fantasies have made him famous – very, very famous – and they look like they might clinch him the Republican nomination.

This is unknown, scary terrain for the establishment staffers of Washington, DC. But Donald is no weird anomaly. Trump is a son and hero to Conspiracy America, a country where academic studies show 40 per cent of citizens believe the US government is covering up the cure for cancer, a republic where 25 per cent believe the “Birther” conspiracy he helped to create, and nearly 20 per cent believe the “Truther” conspiracy that al-Qaeda fanatics were not responsible for the 2001 attack on the Twin Towers. Why do so many Americans believe such fabrications? This is the most urgent question for America today.

The paranoia fuelling Trump’s rise is the curse of the Bush era. Conspiracy America is a delayed reaction to the twin Bush disasters: the War on Terror and the banking collapse. History warns us that fear of demonic plots builds slowly after confusing, traumatic events. And once a conspiracy theory is born – The Protocols of the Elders of Zion, for example, or the power of the Freemasons – it is nearly impossible to kill.

Conspiracies about the Kennedy assassination built slowly, peaking in the 1980s. Germany’s “stab-in-the-back” myth grew only slowly after the Treaty of Versailles, peaking in the 1930s. History warns that paranoia about plots thrives in states which are being delegitimised: whenever they are unable to fulfil their promises – of empire, welfare, or the American Dream – the pattern of history is those losing out see plots, not systems, stealing what was theirs.