Time was when the radical left was the force attacking the Enlightenment basis of western civilisation and challenging the mores and landmarks of day-to-day life. Today, that mantle has passed to the radical right. The most visible expression of this will be the US Republican party’s convention in Cleveland this July, riven by hatred between the Donald Trump and Ted Cruz camps as they struggle to win a contest in which no one candidate has won a clear majority in the primaries.

Who can best express the cocktail of nativism, hatred of foreigners in general and immigrants in particular, fetishisation of the absence of government and its handmaiden, the ultra-free market, all wrapped up in profoundly reactionary views of women, religion and punishment, that constitutes the ideology of today’s US right? It will be hand-to-hand political in-fighting, plumbing new depths of viciousness and possible physical violence. Thus will America be great again.

The scale of the Anglo-Saxon ultra-right’s distance from the interests of real people is disturbing

Neither candidate should be remotely electable in this still great republic and while some of what is being said is commonplace in parts of the deep south, derelict industrial areas, rundown suburbs, rightwing thinktanks and billionaire political backers and media outriders, it is far from the mainstream, where common decencies still rule. But this is not an argument unique to what seems an increasingly foreign country across the Atlantic: the same very rightwing forces are at work in Britain.

A similar ideological cocktail animates the Leave EU campaign in the struggle against mainstream liberal Britain. Trump and Cruz have their counterparts in Farage’s splenetic anti-immigrant nativism, Johnson’s de haut en bas populism, Redwood’s intellectual anti-statism etc. Just as many Americans fear a President Cruz or Trump decisively re-engineering their country and its leadership of the west, so there is a growing apprehension that similar rightwing forces are about to re-engineer Britain and its place in the world for the worse. The scale of the Anglo-Saxon ultra-right’s ambition – and its distance from the interests of real people, real lives, real business, real science and real international interdependencies – is disturbing.

Getting here has been a 30-year journey. You may disagree with mainstream Conservatism, but it has a respectable pedigree. Democracies should have parties of the right that are distrustful of government, pro-enterprise, sceptical of the value of organised labour, anxious to minimise taxation, wary of social experimentation and ethnic diversity. A lot of people think that way and their views must be represented. But for the radical right in the US, that portfolio of views is part of the middle-of-the-road establishment: devotees can even, horror of horrors, cut deals with Democrats in Congress. Reaganite championing of the market and small government has morphed into a libertarianism that is against government in principle.

Europe has been a proxy for a fight between mainstream liberal Tories and the libertarian anti-state outriders for years

Thus Cruz wants to abolish the Departments of Education, Energy and Housing along with the Inland Revenue Service and the Environmental Protection Agency. Progressive taxation is anathema. The dollar should be backed by gold, making the Federal Reserve redundant. One close adviser to Obama told me last week that the government starts with the assumption that any legislative initiative will be vetoed by Republicans whatever its intrinsic merits. Acts of government, or what Cruz calls the Washington cartel, are by definition bad.

Meanwhile, both he and Trump rail against immigration, which they elide with terrorism. Trump wants to round up 11 million illegal immigrants and deport them, along with banning every Muslim from entering the US. Cruz wants to complete the 700-mile fence along the Mexico border: Trump wants to replace it with a wall.

What feeds all this is the belief that America has fallen from greatness abroad, cannot offer rising living standards at home and must guard against a tidal wave of Islamic terrorism. America’s identity is at stake. But there are different answers to building walls and trying to abolish the state and taxation – and which have broader appeal. It is more obvious that a rogue capitalism is the source of America’s ills, not the poor old state, for most people even in the US their lifeline and shaper of opportunities. The idea of checked and balanced democratic government as the expression of the commonweal is the great Enlightenment gift, well expressed in the US constitution, and which mainstream America understands. In this sense, Cruz and Trump set themselves against the founding fathers of their country and its culture.

Labour needs Jeremy Corbyn to do the same job as Bernie Sanders

Thus it should be no surprise that the self-styled democratic socialist Bernie Sanders is challenging Hillary Clinton for the Democratic presidential nomination more effectively than even he could have supposed 12 months ago. He is less a socialist, more an exponent of using smart government actively to serve the common interest, redistribute income and reshape the increasingly dysfunctional institutions of the US economy. He won’t win the nomination, but he is pushing Clinton into much more proactive left positions than she would have otherwise have taken. And she is much more likely to be president than Cruz or Trump. The right, notwithstanding its amazing financial resources, is in the depths of a deep crisis. As it becomes a prisoner of its worst instincts taken to their ideological extreme, it becomes unelectable.

In Britain, David Cameron’s travails have come from wrongly believing that the right is in the political and intellectual ascendancy. The country won’t let its steel industry disappear to “market forces” that are so transparently rigged; does not believe that trusts in Panama can ever be private matters; will not connive in lowering the living standards of the disabled to drive up those of the upper-middle-class. The mass of the electorate are not converts to zero government and libertarianism.

How the referendum will go is more uncertain; a lot will depend on whether Labour and the trade unions can energise their support, and whether business will have the chutzpah to speak out. On balance, Remain will probably win. But win or lose, the result will prompt a crisis in British Conservatism analogous to that in US Republicanism. Europe has been a proxy for a fight between mainstream liberal Tories and the libertarian anti-state outriders for 20 years. Once the result is known, the battle will be on in earnest, with the mutual name-calling already opening up unbridgeable divisions. Labour needs Jeremy Corbyn to do the same job as Sanders: move his party to the left but leave a mainstream variant of Clinton with broad appeal to win in 2020 – and keep on winning. The 30-year rise of the right is over.