Since Donald Trump’s 2024 victory, the Democratic Party has been embroiled in a vicious internal conversation over “moderation.” One camp argues that the party has moved too far to the left on cultural issues, particularly immigration and trans rights, and that it needs to tack to the center in order to secure its long-term political future. Their opponents argue that such a strategy will alienate core Democratic voters without making significant inroads among the MAGA faithful.

This week, the anti-moderation camp has been claiming vindication — citing not developments in the US, but the resignation of UK Prime Minister Keir Starmer.

Starmer has, more than any other center-left politician around the world, actually executed on what the pro-moderation camp proposes — moving the Labour Party to the center on social issues, particularly immigration. Yet Starmer’s numbers collapsed, and Labour experienced a series of humiliating electoral defeats in special and local elections, while the far right and far left both surged. For the anti-moderates, the lesson is straightforward: a Democratic party that does something similar is due to defeat.

“Starmer’s resignation is a warning,” Adam Bonica, a political scientist at Stanford University, wrote this week. “In a moment like this, tacking right isn’t the safe play, it’s the thing that sinks you.”

The moderates, for their part, argue that this is a misread of the evidence: that Starmer actually won power in the first place due to moderate politics, and that his declining numbers after taking power have more to do with economic fundamentals than culture.

“His cultural moderation has been an asset to Labour in getting closer to where the mainstream of voters are,” Claire Ainsley, a former Starmer adviser and current director of Project on the Center-Left Renewal at the Progressive Policy Institute, told me.

The evidence suggests both sides are overstating the case. His rise to power shows the potential upside of moderating; his downfall shows its risk.

Moderation can mitigate problems stemming from a perception that party is too extreme. But it doesn’t always work the way supporters of moderation suggest, with calculated policy concessions on social issues like immigration automatically translating to increased support.

In fact, said policy concessions can end up trapping you into a political no-man’s land without a base of your own to lean on — unless paired with a clear affirmative vision of one’s own.

After the UK’s 2019 elections, the Labour Party was in the wilderness. Led by the hard-left socialist Jeremy Corbyn, the party suffered its worst performance in roughly 100 years.

When Starmer won the Labour leadership contest in 2020, he pursued a strategy that the British political scientist Simon Griffiths described as “decontamination:” a conscious effort to reposition Labour as a party within the UK political mainstream. He apologized for Corbyn’s handling of antisemitism, endorsed an increase in defense spending, and began openly mocking his predecessor as out of touch with ordinary Britons.

“He simply let it be known that the party had changed and was not the same kind of socialist party Corbyn had led,” Griffiths writes in the paper, describing his strategy as “a pursuit of ideological quietism to distance himself from Corbyn and reach out to more socially conservative voters who would be wary of this rhetoric.”

The initial results seemed to vindicate the approach. In the 2024 election, Labour won nearly two-thirds of the seats in the UK parliament, the third-largest majority in the party’s (rather long) history. There’s evidence that Starmer’s moderation helped: Voters who switched from the Conservatives in 2019 to Labour in 2024 were vastly more likely to say the Labour Party respected people like them under Starmer rather than Corbyn.

There are, however, two crucial caveats.

First, it’s not obvious how important Starmer’s relative moderation was in the ultimate outcome. The Conservative Party had been in power for 14 years at that point, and its reputation was in shambles. Data from YouGov, a leading UK pollster, showed that Labour supporters were overwhelmingly more likely to cite getting rid of the Tories rather than affirmatively backing Labour as the chief reason for their vote.

Second, there is little reason to believe that Starmer’s moderation on cultural issues specifically played a decisive role. Neither immigration nor trans rights drove the perception that Corbyn was too radical; Starmer’s “detoxification” campaign focused on foreign and economic policy for a reason. YouGov’s 2024 data shows that Labour voters’ top issues were overwhelmingly economic (cost of living and healthcare).

Starmer, in short, likely benefitted at least somewhat from seeming more moderate than Corbyn. But that has much more to do with a broader, more ideological diffuse branding than his specific stance on immigration or trans rights.

Almost immediately after taking office, Starmer’s numbers began to drop. Nearly everyone agrees on the reason: he failed to deliver the substantive quality-of-life improvements he promised.

“There’s been no respite on the cost of living, with particularly food and energy inflation remaining high, while the NHS [National Health Service] and public services have not really improved,” YouGov’s Dylan Difford wrote this week. Labour “has ignored that many of its most glaring issues are the complaints common across all of their losses — the cost of living, public services, feelings of a lack of delivery and change — the key issues that helped Labour into power in the first place.”

The question, however, is whether his tack to the center on cultural issues mitigated the fall out of these problems — or exacerbated it. The best evidence suggests the latter, particularly when it comes to immigration.

Yet Starmer’s numbers continued to fall. Reform UK — an extreme anti-immigration party — surged, becoming the most popular party in the country and the odds-on favorite in the 2029 election. Disillusioned left-wing voters defected en masse to the Green Party, a former fringe party that took an unapologetically pro-immigration stance.

“They didn’t win back those voters that left for reform — and they alienated progressives,” Tarik Abou-Chadi, a political scientist at Oxford who studies European left-wing parties, told me.

Abou-Chadi, and many others in his field, find that this is a rather common occurrence in European politics. On average, center-left parties who tack to the right on immigration do not tend to win over voters who had previously supported far-right parties. They do, however, tend to lose voters to left-wing parties who have more to offer the cultural left.

There is unusually good evidence that Starmer’s positioning on immigration hurt him in precisely this fashion.

In a recent study, a group of eight researchers measured how a group of voters’ attitudes towards Labour changed after the “Island of Strangers” speech. They found that the speech had some of the intended effect: Voters perceived Labour to be tougher on immigration after the speech than they did before. However, that perception didn’t help the party electorally — and in fact likely hurt it.

The speech “decreased voting intentions for Labour by 1.2 percentage-points and resulted in a 3.9 percentage-point haemorrhage in support from Labour’s own former voters without attracting any new supporters,” the authors conclude.

It’s tempting to conclude that Starmer is a slam-dunk case against the “Democrats need to moderate” position in the United States. I think this is directionally correct, but requires a bit more nuance.

The US and UK political contexts are importantly different. The UK system allows for third parties to run and succeed: not just Reform and the Greens, but also the center-left Liberal Democrats, the Scottish National Party, and the new radical right faction Restore Britain.

In such a system, voters dissatisfied with Labour from the left have options. Left-wing Americans have no such viable option; they either vote for whoever the Democrats nominate or throw their vote away and de facto help the GOP. This makes it less likely that tacking to the center could cost Democrats a huge chunk of their base in the way that it has Labour.

Moreover, the American system gives individual legislators a lot more autonomy than the UK’s disciplined parliamentary system. That means that individual legislators have more room to create individual brands that might benefit from ideological moderation — like Republican Senator Susan Collins in Maine or Democratic Rep. Marie Gluesenkamp Perez in her conservative Washington district.

The most relevant American lesson from the Starmer experience is thus not that moderation is always and forever politically ineffective. It’s that successful moderation is much more complicated than simply picking the positions that appeal most to the median voter and making them your own.

When Starmer’s moderation worked, it wasn’t because he became identified with a specific set of moderate policy proposals. Rather, it was that he cultivated a perception, an ethos, a vibe that Labour was no longer the same party it was under Corbyn. He and his team figured out that the median voter thought Labour was out of touch, and took highly visible actions to correct that perception.

But this didn’t work as a governing approach.

Starmer’s focus on looking for poll-tested cultural policies designed to win over voters lost to Reform was premised on a myth — that large numbers of far-right voters were open to voting for the center-left. Moreover, it necessarily meant compromising one’s own image in ways that made him seem both inauthentic and unprincipled, as if Labour under Starmer were trying to be something it obviously wasn’t and couldn’t be.

Those changes might have been acceptable if there was a new political identity to replace them. But Starmer also struggled to articulate a new North Star for the party, and for his personal brand of politics, that could attract a meaningful and enthusiastic base of support.

“Positioning himself as the custodian of a phantom center, Mr. Starmer treated most Labour supporters with contempt, as a partisan inconvenience and an obstacle to his project of national renewal,” the British journalist Samuel Earle wrote in the New York Times in May. “Yet he has also seemed too nervous to outline what that project might be.”

This might be the most salient lesson for American politics: that whatever one’s ultimate position is, be it left or center, compromising one’s own core identity is almost certainly a losing strategy. Political parties need affirmative visions that both animate their core supporters and create a clear sense of what they are and what they stand for.

Moderate politics can provide that vision: Both Bill Clinton and Tony Blair had versions of it in the 1990s. But Keir Starmer didn’t — and both he and his party are paying the price.