Donald Trump’s actions are often so concerning and bewildering it isn’t obvious how to respond. This has been a week of shocks, building from the revelation that immigrant children were being taken from their carers, through to the president’s tweets yesterday suggesting that the rule of law should be suspended to allow officials to send anyone – even potential refugees – home without due process.

Amid the talk of “infestation”, state-sponsored child cruelty and the administration’s fondness for propaganda, there are valid comparisons to be made with some of the worst regimes of the 20th century. As Rabbi Laura Janner-Klausner said, Trump’s actions could be staging posts on the road to much darker places.

It is often tempting to call Trump a Nazi or a fascist. But is it helpful to do so? Let’s clear a couple of things up first: Trump isn’t a Nazi. Nazis don’t exist any more. Trump is supportive, or at least not unsupportive, of the alt right; a far right and libertarian hybrid. But they’re not Nazis and neither is he. He’s also not a fascist . Trump shows disdain for democratic institutions but he is an elected leader – elected by tens of millions. He seems frustrated by the rule of law and democratic process but he is far, thankfully, from rejecting democracy or advocating a one-party state.

I’m not discounting that in another time Trump would have been a fascist. I think he probably would have. Like the original ’America First’ figurehead, Charles Lindbergh, Trump openly admires dictatorships. But definitions matter. We need to keep a laser focus on what we criticise Trump and his movement for. Because misplaced comparisons can do damage. You lose the trust with the millions of people who don’t strongly object to Trump but are uneasy with his policies, and you set your argument up to fail by making a comparison that can easily be rebutted. Those people then say: I’m not listening as you are over-egging the pudding.

The discussion doesn't end there, though. That’s where it begins. And this is my main point. Societies can’t just be divided into “free” and “unfree” any more than a human can be described as “healthy” or “unhealthy”. Like a body, a state is a hugely complex, interlocking system. That means that certain parts can be working well whilst others are not. It means that pathologies can be localised to one system, but they can also be – at any given time – spreading.

And like anbody, a social pathology can predate visible symptoms by months or even years. In some 20th century states, every aspect was corrupted to make mass killing and oppression possible. The leader, but also parliament (a fig leaf), judiciary (loyal to the leader not justice) and the perverse incentives for individuals to act contrary to their consciences That level of pathology is common to societies run by fascists, communists and Nazis. The name is unimportant. But you can pull the common themes together and see how societies progress towards un-freedom and even genocide.

A few months ago, I helped make a film featuring survivors of three different genocides. Their experiences were as different as you would expect, spanning continents and decades, but they also had much in common: discrimination, dehumanisation, neighbour turned against neighbour, splitting society into tribes and racial hierarchies, propaganda. In each case, the fundamental rights which protect us from the state were dismantled.

So back to Trump. He’s no Nazi or fascist. But he – and his movement – do things that corrode liberal democracy. How can we tell? Human rights. The European Convention on Human Rights was designed by people who understood the pathologies that led to totalitarian states. People like Hersch Lauterpacht , who lost his family in the Holocaust, and David Maxwell Fyfe, who prosecuted at the Nuremberg War Crime trials. They helped create a simple list of rights needed for a free society: fair trial, no torture, freedom of speech…

Human rights laws are a blueprint for a free society, but they are also an early warning system. And breaches of human rights are therefore a useful way of assessing how pathological the behaviour of a leader or government is to the political system they are running.

That’s why we should worry about Trump. He is rhetorically against the idea of human rights. He withdrew the US from the UN Human Rights Council. He rejects international institutions that are the framework for international human rights standards. His anti-Muslim polcies are discriminatory – drawing distinctions between “us” and Islam, so building tribal consciousness which leads to bad places. He speaks of “infestation”– language familiar to that of Goebbels, who compared to Jews to “rats”, and Hutus in Rwanda, who reduced Tutsis to “cockroaches”. He supports the torture of terror suspects and practices that have been outlawed in international human rights law for 40 years. His child separation policy would never have survived a human rights challenge and was rightly seen as crossing a line.

So Trump may not be a Nazi or a fascist but he – and the other populist regimes that are building a power-base across Europe – may still pose a threat to liberal democracy. Human rights can be a litmus test to see the difference between policies and practices we dislike and ones are genuinely corrosive of democracy and may lead to darker places. That’s why it is vital that we protect and strengthen our human rights laws during these concerning times. The film I made about genocide survivors was called The Warning Signs. There are warning signs now which we cannot – must not – ignore.