In a well-ordered democracy the public debate of an election campaign would approximate what Jürgen Habermas projected as an ‘ideal speech situation.’  The Wikipedia definition is concise and accurate:
In an ideal speech situation, participants would be able to evaluate each other’s assertions solely on the basis of reason and evidence in an atmosphere completely free of any nonrational ‘coercive’ influences, including both physical and psychological coercion. Furthermore, all participants would be motivated solely by the desire to obtain a rational consensus.
Under these circumstances, public debate might help the democratic process produce rational government. I say ‘help’ because, for public debate to produce rational government, voters must want rational government. In all these respects, US representative democracy is broken.
Non-rational coercive influences
Over the past year, non-rational coercive influences have been everywhere in evidence in US politics and society.
The US state does not publish data on killing of civilians by police, but the Guardian newspaper does. Blacks are more than twice as likely to be killed than whites, and Native Americans three times as likely. And yet with about three killings a day, over the period 2005-15, as reported in Huffington Post:
[T]here have only been 13 officers convicted of murder or manslaughter in fatal on-duty shootings. 
This, of course, is the context in which the Black Lives Matter movement developed, offering:
[A]n ideological and political intervention in a world where Black lives are systematically and intentionally targeted for demise. It is an affirmation of Black folks’ contributions to this society, our humanity, and our resilience in the face of deadly oppression. 
The seeming licence with which police practice violence upon Native Americans and people of colour, is reinforced by the militarisation of the police force, relying particularly upon the gift of surplus materiel to the police after the withdrawal of US ground troops from Iraq.
The New York Times reports not only that local police forces are becoming more militarised but that this is also changing their way of engaging with the citizens they serve and protect:
The equipment has been added to the armories of police departments that already look and act like military units. Police SWAT teams are now deployed tens of thousands of times each year, increasingly for routine jobs. 
Trump’s Law and Order Ideology
During the election campaign the Trump campaign suggested that the police forces in the USA were unfairly criticised and he was, according to the Boston Globe:
[U]nwavering in his support of police officers. 
Trump promised his support to a Blue Lives Matter Bill that would make violence against the police a hate crime, mandating a ten-year sentence for anyone who physically harms a police officer, and life for attempts to kill, kidnap or sexually abuse a police officer. Despite the asymmetry of violence and physical resources, the Trump campaign presented the US as a place where violence against the police is unrestrained and in his speech accepting the Republican nomination, Donald Trump talked this up:
I have a message to every last person threatening the peace on our streets and the safety of our police: When I take the oath of office next year, I will restore law and order to our country. 
Law and order is central to Trump’s electoral appeal. In an article in New Republic, Jeet Heer identified the coherence that fear and discipline gave to Trump’s signal issues:
Crime links together the various strands of Trump’s politics that might otherwise be diffuse: immigration (enforcing the law at the border), racial resentment (supporting police in the age of Black Lives Matter), foreign affairs (a tough military stance being a form of international crime control), and partisan politics (‘Crooked Hillary’ being an imagined criminal). 
The Law and Order ideology compromises the ideal speech situation in two ways. First, it isolates social enemies. Trump began his campaign playing upon this string:
The U.S. has become a dumping ground for everybody else’s problems. […]. When Mexico sends its people, they’re not sending their best. […] They’re sending people that have lots of problems, and they’re bringing those problems with us. They’re bringing drugs. They’re bringing crime. They’re rapists. And some, I assume, are good people. 
By increasing the suspicion of marginal groups, Trump encouraged his supporters to demonise people of colour and implied that the election might be stolen by fraudulent voting in African-American city districts:
But take a look at Philadelphia, what’s been going on, take a look at Chicago, take a look at St. Louis. Take a look at some of these cities, where you see things happening that are horrendous. 
Targeting people of colour in a context where physical violence against them by police is both common and unpunished could certainly be expected to discourage their political participation, either in public assembly or in public voting.
In the second place, the Law and Order ideology demonises not only marginal groups but also dissenting arguments. At one rally, a heckler was being taken out when, as Ben Schreckinger reported, Trump interjected:
‘The guards are being very gentle with him,’ Trump said. ‘I’d like to punch him in the face, I’ll tell you that.’ […] ‘We’re not allowed to punch back any more,’ Trump lamented. The billionaire said he missed the ‘good old days’ […]. ‘You know what they used to do to a guy like that in a place like this?’ Trump said. ‘They’d be carried out on a stretcher, folks.’ 
Trump does not seem to like contradiction and questions the motives of unflattering press coverage. Schreckinger was banned from Trump events for an unflattering article on Trump’s first campaign manager, Corey Lewandowski. Trump dismissed this journalist as:
[A] dishonest, third-rate reporter. 
This was in March and by June the news outlets excluded from Trump events included BuzzFeed, Politico, the Daily Beast, Univision, the Huffington Post, and the Washington Post. 
The election presents an existential threat. With, among other things, several Supreme Court nominations likely to fall to the next President, Trump could present the election as the last stand for conservative, mainstream USA. Late in the campaign, Donald Trump tried to mobilise his vote by scaring supporters at a rally in Council Bluffs Iowa, with this:
If we don’t win this election, it will never ever happen….we will never have a shot — this is it. The tables will be turned and it will be too late. 
This is not a matter of Trump’s personal beliefs but rather of what matters to his supporters, what is sufficient spur to their participation. If certain values pose an existential threat, then, those values and arguments have no place in the public arena.
The US has experienced this sort of censorship before; it was called McCarthyism. A recent article in the New York Times, linked Trump to Joseph McCarthy’s chief legal adviser, Roy Cohn.  Cohn gave Trump an introduction to the elite of New York politics and real estate. He also advised Trump on how to use the law and publicity to develop his business interests.
Conspiracy theories are central to the Trump ideology. As one recent article notes, McCarthy relied on one central conspiracy (the Communist plot) whereas Trump finds dozens to engage him:
Trump’s position is that our government is […] a fraud, and thus he feels free to debase the electoral system. 
Another of Trump’s supporters, Newt Gingrich, explicitly asks for the return of the House Un-American Activities Committee:
‘We originally created the House Un-American Activities Committee to go after Nazis,’ he said during an appearance on ‘Fox and Friends’ this week. ‘We passed several laws in 1938 and 1939 to go after Nazis and we made it illegal to help the Nazis. We’re going to presently have to go take the similar steps here.’ 
Gingrich wants an ideology test to deal with the threat of Islamic extremism.
So, the Trump campaign talked up a sense of crisis in American democracy and society. It demonised those whom it identified as threats to conservative America. It treated its opponents as evil or criminal. It encouraged violent feelings against them. It restricted the press. It suggested that the police were being unfairly criticised and that repressive policing was urgently needed to deal with the internal and external threats from illegal immigrants, Islamic terrorists, and lawless African-Americans. This was a rich suite of non-rational coercive influences preventing the election enjoying anything like an ideal speech situation.
Beyond these circumstances, it is also clear that the desire to obtain a rational consensus was likewise weak or absent from much of the campaign. This feature of the election elicited extensive commentary and several now speak of post-truth politics. One report categorised fully 70 per cent of Trump’s public statements as untrue.  The political effectiveness of a statement is judged by the emotions it arouses rather than by its veracity. This is true even among supporters who were moved by the emotion. They, too, seem to understand that things are said for effect and not out of conviction. Thus supporters will accept lying to the press, even lying in front of an audience simply because the remarks are (again) being reported in a press that is owed no honesty. Trump’s first campaign manager, Corey Lewandowski explained to reporters that it was their naïveté that was exposed:
‘You guys took everything that Donald Trump said so literally,’ he said. ‘The American people didn’t. They understood it. They understood that sometimes — when you have a conversation with people . . . you’re going to say things, and sometimes you don’t have all the facts to back it up. 
For Trump supporters, the principles of politics are selfish rather than normative. In a recent discussion of the election, Trump’s second campaign manager, Kellyanne Conway, tried to explain why the furore about racism would not alienate his supporters:
There’s a difference to voters between what offends you and what affects you. And they were being told constantly, ‘Stare at this, care about this, make this the deal-breaker once and for all.’ And they were told that five or six times a week about different things. And yet they went, they voted the way voters have always voted: on things that affect them, not just things that offend them. 
That’s as clear a statement of the effectiveness of cultivating selfishness as I have read.
Furthermore, neither a political promise nor a political statement is irrevocable. Trump notoriously tweeted that:
The concept of global warming was created by and for the Chinese in order to make U.S. manufacturing non-competitive. 
Consequently Trump stood up for coal mining, for fracking and pipelines, and promising the jobs that would come with these fillips to the hydrocarbon economy. This was enough for most of the miners of West Virginia, for example, who promised their votes to Trump.  Trump had promised to renege on the commitments the US undertook as part of the Paris climate accords, yet, in an interview after his victory he took a very different tack:
On climate change, Mr. Trump refused to repeat his promise to abandon the international climate accord reached last year in Paris, saying, ‘I’m looking at it very closely.’ Despite the recent appointment to his transition team of a fierce critic of the Paris accords, Mr. Trump said that ‘I have an open mind to it’ and that clean air and ‘crystal clear water’ were vitally important. 
The earlier certainty was needed in order to dismiss the environmentalists. Given the extensive scientific research on climate change, it really isn’t adequate to claim to have allowed your mind to remain fully open, as one journalist implied:
When you say an open mind, you mean you’re just not sure whether human activity causes climate change? 
Trump’s reply is instructive:
I think there is some connectivity. There is some, something. It depends on how much. It also depends on how much it’s going to cost our companies. You have to understand, our companies are noncompetitive right now. 
So, the truth of claims about Climate Change is to be set by the pragmatic consideration of who pays, and how much? Cynical and selfish, but, that’s post-truth politics for you.
Gerry Kearns, 4 December 2016
 Jürgen Habermas, The Theory of Communicative Action. Vol. I: Reason and the Rationalization of Society, trans. T. McCarthy (Boston: Beacon Press, 1984 ).
 Matt Ferner and Nick Wing, ‘Here’s How Many Cops Got Convicted Of Murder Last Year For On-Duty Shootings,’ Huffington Post (13 January 2016).
 Matt Apuzzo, ‘War Gear Flows to Police Departments,’ New York Times (8 June 2014).
 Michele McPhee, ‘The hidden Trump voter — the police,’ Boston Globe (9 November 2016).
 Perry Bacon, ‘Trump and Other Conservatives Embrace “Blue Lives Matter” Movement,’ NBC News (23 July 2016).
 Jeet Heer, ‘Trump’s “Law and Order” Speech Was Full of Lies. It Just Might Work,’ New Republic (22 July 2016).
 Ian Schwartz, ‘Trump: Mexico Not Sending Us Their Best; Criminals, Drug Dealers And Rapists Are Crossing Border,’ Real Clear Politics (16 June 2016).
 Trip Gabriel, ‘Donald Trump’s Call to Monitor Polls Raises Fears of Intimidation,’ New York Times (18 October 2016).
 Ben Schreckinger, ‘Trump on protester: “I’d like to punch him in the face,”‘ Politico (23 February 2016).
 Seth Stevenson, ‘A Week on the Trail With the “Disgusting Reporters” Covering Donald Trump,’ Slate (20 March 2016).
 ‘Editorial: The slippery slope of censorship under Trump,’ Daily Iowan (15 June 2016).
 Editor, ‘Trump: “If we don’t win, it will be too late,”‘ Webmarked News (28 September 2016).
 Jonathan Mahler and Matt Flegenheimer, ‘What Donald Trump Learned From Joseph McCarthy’s Right-Hand Man,’ New York Times (20 June 2016).
 Carlisle Ford, ‘Joseph McCarthy and Donald Trump: a shared contempt for democratic institutions,’ MinnPost (17 October 2016).
 Laura Clawson, ‘Gingrich proposed bringing back House Un-American Activities Committee,’ Daily Kos (11 November 2016).
 William Davies, ‘The Age of Post-Truth Politics,’ New York Times (24 August 2016).
 I have explored some of these issues in a blog on Pundits and Scholars (27 May 2013).
 Ruth Marcus, ‘Welcome to the post-truth presidency,’ Washington Post (2 December 2016).
 Tamara Keith, ‘Bitterness Overwhelms As Trump And Clinton Campaign Staffers Face Off At Harvard,’ NPR (2 December 2016).
 @realDonaldTrump tweet, 6 November 2012.
 Declan Walsh, ‘Alienated and Angry, Coal Miners See Donald Trump as Their Only Choice,’ New York Times (19 August 2016).
 Michael D. Shear, Julie Hirschfeld Davis and Maggie Habermas, ‘Trump, in Interview, Moderates Views but Defies Conventions,’ New York Times (22 November 2016).
 ‘Donald Trump’s New York Times Interview: Full Transcript,’ New York Times (23 November 2016).