The acquittal of Donald Trump reminds us once again of the fragility of American democracy. The failure of impeachment along blatantly partisan lines means that the crucial barriers protecting us from authoritarianism cannot be relied on. The fate of the country’s institutions are left to the mercies of a man singularly unfit to safeguard them.

The slow creep of authoritarian rule need not be dramatic. It can even, as impeachment seemed at times, be rather boring. Democracy can die by inches, with precedents being established and barriers swept away so gradually that we don’t see what is happening until it is too late. Historians may look back on the past few years as just such a time, with today’s acquittal bringing to maturity a process from which American democracy may take a long time to recover.

It might not even be Donald Trump who consummates the transition. The changes he has wrought over Republican politics will encourage his successors to follow in his footsteps. Horrifyingly, these successors may even be intelligent and competent, unlike their forefather. The right has entered a permanent war footing in which everything – especially truth and principle – is subordinated to the quest for total victory. Perhaps this army will stand down once Trump leaves the scene, or there will be no new general to take up its banner. It seems unlikely.

But the immediate danger is posed by Trump himself and his enablers. The US Senate majority’s collective shrug in the face of Trump’s crimes rips away the final theoretical restraint on his actions. Alan Dershowitz, one of Trump’s lawyers, went so far as to claim that the president can legally do anything in pursuit of his own re-election if he believes that doing so is in the public interest, almost as if Trump really could shoot someone on Fifth Avenue provided that person was on their way to vote for a Democrat.

Dershowitz later attempted to clarify his remark by saying that it wouldn’t apply if the president’s act was specifically prohibited by law. This was a strange clarification given that Trump did in fact violate the law when he withheld aid to Ukraine, and Trump anyway has previously claimed that the constitution gives the president the power to do “whatever I want”. Before his acquittal, these bizarre theories of executive power have been just that – theories. Now they carry the force of precedent.

A theory of executive supremacy, a supine legislature, and a credulous, adoring segment of the population are the ingredients that authoritarianism is made of

The abjectness of the Republican party compounds the danger. If they stuck by the president through the Ukraine affair they will stick by him through anything. They have acted like the totalitarian functionaries who Hannah Arendt said view the difference between truth and falsehood as something which “depends entirely on the power of the man who can fabricate it”. And while they may have the power to fabricate “truth” for those living in the rightwing media bubble, to everyone else – including the 71% of the public who wanted the Senate to call witnesses – their disconnect from reality has been cringeworthy.

A theory of executive supremacy, a supine legislature and a credulous, adoring segment of the population – which does not need to be a majority – are the ingredients that authoritarianism is made of. Because he certainly isn’t restrained by principle, the fate of American democracy now rests on the question of whether Trump knows the right way to mix the ingredients together.

By far the greatest risk will come in November. We know by now that the standard rightwing playbook calls for painting the Democratic nominee as a dangerous radical hellbent on destroying America, and claiming that millions of “illegals” voted for them, rendering the election result void. Imagine this rhetoric unfolding as Trump endures a narrow electoral loss and refuses to concede. Can we have any faith that a Senate and a US supreme court in the hands of his servants will show him the door?

Arendt also understood that those who use their power to construct a world of falsehoods for their supporters eventually have to destroy the power of those who would challenge it with the truth. This is why lies are so dangerous in a democracy, and it is why Trump and his allies systematically attack all independent sources of factual authority in society: the media, the civil service, the law. Elections, which force would-be tyrants to face up to the authority of the greater part of the public which does not live in their dreamworld, are perhaps the greatest threat of all. That is why Trump cannot help but try to subvert them, and it is why he will inevitably do so again.

None of this means that impeachment was a mistake. Like acquittal, a failure to impeach at all would have sent the same signal: that there are no limits on Trump’s actions. Impeachment at least kept the torch of the truth and the law alive. But now we must be very careful. They are about to – they must – come to try to extinguish that torch. Only an electoral repudiation so vast that it cannot be questioned can prevent them, and it must be won at a time when their power has never been less restrained by law or principle. The fate of democracy in America depends on it.