Deus ex machina was the ancient Greek theatrical convention of resolving the unresolvable by crane-lifting a god on to the stage to make everything better again through divine fiat. Right now, a bit of deus ex machina sounds pretty sweet.

Many people hoped that special counsel Robert Mueller’s Russia probe would play that role in the US. Its conclusions would be so damning as to sweep away the knotty problem of Donald Trump without the grinding task of finding support for a different president next year. But it was never likely that congressional mathematics would allow impeachment, nor even that Mr Mueller’s report (assuming we ever get to see it) would contain anything to sway anyone either way. We all, surely, know what we think about Mr Trump by now.

In the UK, some Remainers have been hoping the divine plot twist would be supplied by a record-breaking petition. Almost 6m people have demanded that the UK revoke Article 50 and walk out of the Brexit tragedy before the final act. On Tuesday, the government gave its response: get lost, Citizens of Nowhere. (I paraphrase.) Perhaps the following day’s “indicative votes” in parliament would resolve things? They were indicative of something, at least: gridlock.

Still, change can happen, and sometimes with astonishing speed. A few years ago, the project of Brexit was the pipe-dream of a few obsessives. The percentage of Britons naming EU membership as the most important issue was in the low single digits. Now Brexit is the official goal of the two largest political parties, albeit one they are finding it rather hard to hit.

Similarly, the changes that Mr Trump has wrought upon American and global politics are too numerous to list. True, most of them are changes for the worse — but it is hard to make the claim that stasis is inevitable.

What explains this curious sense that we are somehow dealing with chaotic change and futile stasis all at once? One explanation — offered in Cass Sunstein’s recent book, How Change Happens (UK) (US) — is what he calls “partyism”. The name deliberately echoes vices such as racism and sexism; Professor Sunstein argues convincingly that many of us now dismiss entire groups of people on the basis of their political affiliation.

For example, views of interracial marriage have become dramatically more tolerant. Yet cross-party marriage is now beyond the pale for many. Prof Sunstein reports that in 2010, about 49 per cent of Republicans and 33 per cent of Democrats would feel displeased if their children married outside their political party — up from about 5 per cent in 1960. A similar trend has taken place in the UK.

Political scientists Shanto Iyengar and Sean Westwood used a common (if controversial) measure of subconscious bias, the “implicit association test”, to examine partyism. They found party affiliation produced stronger measures of implicit bias than did race.

One might argue that there is nothing intrinsically wrong with partyism. Rather than unjustifiably judging people based on their gender or ethnicity, we justifiably judge them for the choices they have made. Still, an environment where parties command unswerving support from their own base and unswerving loathing from the opposition is not one conducive to rational discussion. That, perhaps, accounts for the feeling of stasis: we feel that nobody is listening and nobody wants to compromise.

Despite the sense of gridlock, it is clear that dramatic change is possible. A hostile takeover of an existing party structure can turn partyism from a force for inaction into a force for radical change. The Brexiters have managed it, as has Jeremy Corbyn, the leader of the Labour party, and, most spectacularly, Mr Trump.

Existing political parties aren’t the only agents of change. In countries where the voting system permits it, new parties have surged forward. Even in the UK, where the electoral system gives an enormous advantage to large established parties, Leave and Remain have become stronger sources of political identity than traditional parties.

Outside the realm of traditional politics, consider the #MeToo movement — a catalyst for a dramatic and overdue reassessment of what behaviour society will tolerate from powerful men.

These changes are so sudden because we are social beings. We often don’t know how we feel until we see that other people are taking a stand. It seems that nothing is changing and nothing will ever change until a critical threshold is reached, and the dam bursts. Issues that were ignored become salient. We go from shrugging our shoulders to marching in the streets. These changes are unpredictable, and we often mislead ourselves after the fact into thinking that they were inevitable all along.

This, then, is the process of political change: long periods of stasis, sudden bursts of activity, and a good deal of luck. Behind it all, a long slog of persuasion, mobilisation and frustration — less a glorious pilgrimage than an endless treadmill. No wonder most of us would prefer divine intervention.

Written for and first published in the Financial Times on 29 March 2019.

My book “Fifty Things That Made the Modern Economy” (UK) / “Fifty Inventions That Shaped The Modern Economy” (US) is out now in paperback – feel free to order online or through your local bookshop.