In 1981 several senior figures in the British Labour Party decided that they could no longer stomach the policy positions being foisted on them by a radicalised membership. Because they could not control their party, they would, they decided, set up a new one – and so the Social Democratic Party was born. Labour is unlikely to split again despite the fissures of the past year, but could something similar happen in the United States?

Three times over the past 15 years senior, moderate Republicans have left the party: the Vermont senator Jim Jeffords in May 2001, the one-time Rhode Island senator Lincoln Chafee in 2007 and the Pennsylvania senator Arlen Specter in April 2009. Yet these were isolated incidents and failed to produce an alternative party. Today, as the Grand Old Party veers ever further to the right, one can only hope that a broader group of moderates will, in a co-ordinated act, try to create something new.

Last month, the South Carolina senator Lindsey Graham was asked whether he would prefer Donald Trump or Ted Cruz as his party’s presidential nominee. He replied, “It’s a lot like being shot or poisoned. I think you get the same result.” Graham, a heavyweight in the Senate, was expressing a fear that he shares with a growing number of senior Republican politicians. Trump, whose snarling, coarse and xenophobic persona plays so perfectly to his support base, comes closer to representing an American version of fascism than any major US political personality of recent decades. Cruz, whose Bible-thumping, take-no-prisoners hyper-conservatism has the potential to alienate anyone remotely moderate (the conservative New York Times columnist David Brooks described his attitudes as “pagan brutalism”) has enthused the equally infuriated fundamentalists who make up a significant slice of the Republican vote.

Then there is Ben Carson, whose statements to date suggest a blend of low-key ignorance and unremitting extremism. In state after state, the three most ferocious of the GOP candidates command between them the support of about 60 per cent of all Republican voters. In some states, such as South Carolina, they command even more.

All three argue for a foreign policy that uses the carpet-bombing of entire regions and increased deployment of “enhanced interrogation techniques”. They demand, or have expressed sympathy for, the exclusion, registration or surveillance of Muslims and trot out accusations about fifth columnists and traitors. Theirs is a language of violence, of the pogrom, of scapegoating and of fear. They compete with each other to show who can build a bigger wall to enclose the Land of the Free. They reject the science of climate change, propose tax policies that would gut non-military parts of the federal government and advocate policies that would create a vicious trade war with the Chinese.

The Republican Party, hoist by its own petard after years of rightward drift – of shutting down government when it didn’t get its way; of taking the country repeatedly to the verge of default on its debt obligations; of speaking a barely coded racial language in its critiques of President Obama; of playing to the Tea Party to oppose health-care reforms; of tolerating, if not encouraging, Islamophobia – seems incapable of stopping the madness. That madness, which the party grandees thought they could channel, has now burst the banks within which it was contained.

Lindsey Graham doesn’t like what he sees. One doubts that John McCain – whom Donald Trump called a “loser” because he was captured and tortured during the Vietnam War – does, either. A moderate senator such as Maine’s Susan Collins must surely be aghast at what her party has become, dreading the prospect of spending the next year defending a manufactured constitutional crisis around the confirmation of a Supreme Court justice while drumming up support for Trump or Cruz.

At least six GOP senators up for re-election this autumn in competitive states such as Ohio and Pennsylvania must realise the implications of alienating moderate voters. Similarly, the more pragmatic Republican governors in the Midwest, who have spent years convincing people that they know how to get things done, must be losing patience with the government-paralysing actions of the leadership in Washington, DC.

How nice it would be if they found the courage collectively to walk away from a party that is flirting with the most ghastly forms of intolerance. It probably won’t happen but, at this point, as the party of Abraham Lincoln devolves into the dark, paranoid world of Trumpism, it should.