Free speech will be under challenge following the emergence of Donald Trump as the candidate presumptive for the Republican Party in the forthcoming presidential election in the US.

Already the US Left has disrupted Trump rallies. In Fort Wayne last Sunday, in the lead-up to the Indiana primary, Trump supporters (including military veterans) were accosted by young children shouting obscenities while adults made rude gestures. The aim of the protesters was to shut down debate.

The presence of middle-class radicals in the protest was evident in a sign held by one protester that read: “Subvert the Dominant Paradigm”. Translated from academic jargon, this means: “Down with Trump”. Or something like that. Meanwhile, the presumptive Republican candidate has called on Americans to board the Trump train — all the way to November 8.

As in many Western democracies, the political situation in the US is fluid. Those commentators, many presenting themselves as experts, who predicted that Trump would never head the Republican ticket were foolish. It is also foolish to prophecise that Trump will never be president. The presumptive Republican candidate has a certain appeal to those sections of the US middle class and working class who feel they have been marginalised by the economic changes of the past decade or so.

According to the opinion polls, Trump trails likely Democratic Party candidate Hillary Clinton.

However, neither presidential contester is popular and it is still six months to polling day. In the quickly moving political climate, it is impossible to predict what will be the atmosphere in the US in early November. One or more suicide/homicide attacks could change the situation dramatically.

There may or may not be a terrorist attack in the US anytime soon. But there are likely to be a ­series of left-wing demonstrations against Trump. The more violent they are, the more they will assist the Republican cause.

The Left’s addiction to expressive politics invariably results in unintended consequences. Any attempt to “subvert the dominant paradigm” by violent means could well make populist Trumpism dominant in the US.

Violent demonstrations aside, the Left in the US and elsewhere is intent on silencing the voices of conservatives. Addressing a graduation ceremony at the University of Michigan last week, former New York City mayor Mike Bloomberg called on US universities to be open to the free exchange of ideas. This week, Virginia Tech withdrew an invitation extended to African-American conservative commentator and author Jason Riley on account of his political views.

Bloomberg was particularly critical of the creation of what are called safe spaces on US campuses. A so-called safe space is a desig­nated location in which certain views on race, or identity, or history cannot be heard. Under this scheme, students are to be kept safe from hearing conservative opinions. Bloomberg, who is a liberal in the US sense of the term, was heckled by some students when he said universities should be open to a wide discussion of opinion.

In Australia, the concept of safe spaces is yet to be advanced. However, it is difficult if not impossible for any senior Coalition politician to address a function at many of Australia’s taxpayer subsidised universities. In recent times, Foreign Minister Julie Bishop, Industry Minister Christopher Pyne and Education Minister Simon Birmingham have experienced violent actions aimed at preventing them from speaking on campuses or elsewhere.

Sections of the green-Left in Australia are intolerant of hearing views with which they disagree. This extends to organisers of taxpayer-subsidised literary festivals. Obviously, such genteel types do not shout down their opponents. They just don’t invite them in the first place.

The 2016 Sydney Writers Festival opens on May 16. The core funders of this event are Arts NSW, Creative City Sydney and the Australia Council of the Arts. That is, the NSW government, the City of Sydney and the commonwealth government. In other words, the Sydney Writers Festival is heavily dependent on taxpayer funding.

The festival’s major partners include the University of NSW, the University of Technology Sydney, Macquarie University, Western Sydney University, the University of Sydney (all taxpayer subsidised) along with The Sydney Morning Herald.

The organisers of the 2016 SWF have used taxpayer funding to put on what can only be called a left-wing stack.

SWF artistic director Jemma Birrell declared in the Herald last month that “Sydney will transform in May with authors and ideas flooding the city”. Sure, some interesting authors will address the SWF, particularly in the area of fiction.

However, in the areas of history, politics and economics, the program is replete with left-of-centre types. Take the Australian contingent, for example. The Spectator’s editor Rowan Dean gets a gig as does The Australian’s Greg Sheridan. But that’s about it. Just a few conservatives to match the SWF’s conga line of leftists.

The left-of-centre speakers include Phillip Adams, Larissa Behrendt, John Birmingham, Frank Bongiorno, Anna Broinowski, Bob Brown, Bryan Brown, Julian Burnside, Jane Caro, Michael Cathcart plus Anna Clark. And that’s just the A, B and Cs. Other speakers include Tim Flannery, Robert Manne, David Marr and Gillian Triggs.

It’s much the same with the Bellingen Readers and Writers Festival, which starts on June 9. One of the “highlights” of the Bellingen festival will occur when leftist activist Irina Dunn interviews leftist favourite Tony Windsor about his candidacy for the seat of New England in the federal election. Needless to say, the voice of Deputy Prime Minister Barnaby Joyce will not be heard at this ratepayers’ subsidised event. In fact, there does not appear to be one conservative on the program.

The contemporary Left in the West has embraced the old adage of the authoritarian that “error has no rights”. In the US, the likes of Trump are to be shouted down while on campuses certain conservative views are ruled out of order.

Aspects of both acts of silencing are found here. In Australia, some leftists censor by not inviting conservatives to turn up, even though the excluded are paying for such ideological self-indulgence with their taxes.