Across the United Kingdom yesterday, protests against US President Trump’s ‘Muslim ban’ erupted, channelled by Prime Minister Theresa May’s hasty invitation to the President for a state visit. Along with chants and outrage there were the usual very British signs: hand-written slogans like ‘Down with this sort of thing,’ ‘I’m really quite cross now’ and, my favourite — from the Cambridge march, naturally — ‘Mr. Trump doesn’t seem like a particularly pleasant gentleman.’ To say nothing of the Scottish placards, which are an art form unto themselves (‘yer maw was an immigrant you absolute roaster’).

Later in the evening, there was a tragic irony when Mr. Trump’s press secretary, Sean Spicer, apparently tried to score political points off the attack on a Quebec mosque, saying it revealed why the President had to be vigilant about security – only to have us subsequently discover the shooter was a far-right follower with Trumpian sympathies.

Only weeks before, Europe’s far-right leaders had gathered in the German town of Koblenz to celebrate a year of victories. They toasted Brexit and Donald Trump’s election as inaugurating a wave of populist revolt. With elections coming up this year in Germany, France and the Netherlands, and with far-right parties surging in all three countries, 2017 looks set to be the year that the old order crumbles.

Or, perhaps not. It may well end up being the year that the populist wave crests, or even subsides a little. Until now, the Western world’s far-right politicians have been able to maintain the purity of the powerless – making bold promises and deriding the compromises of those in power. Now that they have started to occupy the thrones, they will increasingly be judged by their actions. And hugging up Brexit and Donald Trump, which seemed obvious amid the euphoria of their triumphs, may eventually hinder the populists as the messy work of translating words into deeds unfolds.

In Britain, I have written that the easy part of the Brexiteers’ ride is now over. From here on in, it only gets more difficult. The promises they made their followers will one after another be downgraded. Equally with the Trump administration. Saying you’ll ban Muslims from America may play great on the campaign trail. But when you actually do it, as we’ve seen, you tie up the government in crisis-management and impede its movement on other priorities.

Moreover, as the populists run the risk of weakening support, their actions galvanise the opposition. Indeed, it may turn out that with a friend like Mr. Trump in the White House, Europe’s right-wing rebels need enemies. Already Mrs May’s trip to Washington last week, which was feted in the Tory press for all of a day, has turned into something of a liability. The Brexiteers maintain that the free-trade deal Mr Trump promised them will be worth the embarrassment. However, given the time his administration must spend just fighting its own forest-fires, let alone the long list of domestic priorities it has yet to address, they probably overestimate their importance in Washington

One swallow doesn’t make a spring, of course, but there are early signs that doubts about the populist wave are rising on the continent. In Germany, recent polls suggest that support for the far-right Alternative for Germany may have peaked late last year. In France, the liberal and pro-European Emmanuel Macron has electrified the presidential campaign. There are still nearly three months to go, but it is conceivable the progressive vote in France may now coalesce around him and thwart the rise of the National Front’s Marine LePen.

In the Netherlands, the far right does appear to be holding its ground. Although it won’t claim power, since other parties refuse to enter a coalition with it, it may yet emerge as the largest party in parliament. However, that may testify less to its popularity than to the fragmentation and disorganisation of the left.

Everywhere the populists are rising, their strength is inflated by the crisis on the left. In many countries, left-wing parties have descended into internecine squabbling between the neoliberal establishment and what can be called Keynesian nostalgists. Neither offers a plausible or desirable alternative. So even though the far right seldom garners the support of more than a third of the electorate, its tight organisation allows it to set the agenda. At a time when we are constantly looking for lessons from 1930s Germany, that is probably the one we should take away: divided, we fall.

It may be that revulsion at Donald Trump finally galvanises the left to bury its differences and forge a common path ahead. However, as Hillary Clinton’s failed campaign revealed, ‘I’m not him’ is not a very inspiring slogan. The left is taking to the streets and feeling positive again, but it needs a new story to give people, one that goes beyond simply saying how awful its foes are.