Sweden’s Social Democrats are one of the most successful political parties in modern history, winning the highest share of the vote in every national election for the past 100 years. But on Sunday, the once-dominant party scored its worst election result in generations. Its decline is a symptom of when liberal parties let radical-right populists dictate the political agenda.

The Social Democrats won a little over 28 percent of the vote, the most of any party but far short of giving their center-left bloc a majority. Meanwhile, the far-right Sweden Democrats won 17.6 percent of the vote in its best ever result. An exit poll showed that almost a fifth of the far-right voters cast their ballots for the Social Democrats the last election.

The result gives no party a clear route to forming a government, leaves the country politically fragmented and means that the ruling Social Democrats could potentially lose power.

The liberal party’s losses are at least partly self-inflicted. Faced with growing support for the Sweden Democrats, the Social Democrats focused much of their campaign on issues such as immigration and crime, where the far-right controls the narrative. And rather than countering the Sweden Democrats’ anti-Muslim, anti-immigrant rhetoric with a vision of their own, the liberals shifted to the right with proposals that included sending the army into neighborhoods with high crime rates.

“They adopted the [Sweden Democrats’] agenda because they were afraid of losing voters,” said Ulf Bjereld, a professor at Gothenburg University and an active member of the Social Democrats.

“It was a political mistake.”

TT News Agency / Reuters Sweden Democrats party leader Jimmie Akesson gives a speech in Landskrona, Sweden, on Aug. 31, 2018.

The Sweden Democrats, which have origins in the neo-Nazi movement, have spent years telling Swedes that their country is in crisis. The party blames hordes of migrants for breaking the country’s beloved welfare state, bringing in crime and threatening Swedish identity.

That message has resonated with a growing number of people in recent years, as concerns rose over high-profile incidents of gang violence, an influx of refugees and regional economic inequality. Even some of their radical proposals and views found their way into the public debate. In June, a lawmaker’s comments that Jews and indigenous people don’t count as true Swedes received widespread attention. Similarly, the party’s proposal to only take in asylum-seekers from Nordic nations is a de facto ban on refugees that goes against Sweden’s history as one of the world’s most humanitarian nations.

The far-right party further benefited from establishment parties’ lack of attention to its rhetoric. That silence, experts say, created an information vacuum that the Sweden Democrats filled with anti-migrant, ethnonationalist views

“If nobody is talking about stuff that people see as problems, the only answers and understanding that they’re going to have are the ones offered by the populist parties. That’s what you basically had in Sweden,” said Sheri Berman, a professor of politics at Barnard College.

The far-right’s claims, experts say, often did not match reality. Although Sweden has real struggles with regional inequality, social change and increasing violence, overall crime rates have dropped, the country is witnessing the highest economic growth in decades and income has increased across the board. The number of killings has risen in recent years, but there were still only 113 murders last year out of a population of nearly 10 million people, and there have been similar peaks since the government began reporting those statistics in 2002. As for Sweden Democrats’ warning of the “Islamization” of Sweden, the average Swede vastly overestimates the percentage of the population that is Muslim.

When the Social Democrats finally did address public concerns over immigration and crime during the campaign earlier this year, the party mimicked many of the talking points and policies of the far-right. The government’s finance minister suggested refugees seek another country in which to claim asylum, while Prime Minister Stefan Löfven announced that the country would crack down on criminals, and the party declared that emergency border security laws from the height of the refugee crisis would be kept in place indefinitely.

But embracing more conservative policies backfired ― support for the Social Democrats dropped even further, and one member of the Swedish parliament resigned from the party in protest.

“A strategy that was tried to win back voters from the Sweden Democrats meant that the Social Democrats fell even more,” said Bjereld.

“The parties who have been true to their ideological grounds ― they are the only parties who have raised in support.”

JONATHAN NACKSTRAND via Getty Images Swedish Prime Minister Stefan Löfven addresses an election campaign rally attended by Spain's prime minister in Enkoping, Sweden, on Sept. 5, 2018.

That same scenario has played out similarly in countries across Europe, where traditional left and right parties have employed similar strategies to regain voters from populist parties, largely without success.

“What happens is that xenophobia, racism, anti-immigration ideas become more recognized and legitimate ... because the big parties, the power-holding parties are jumping on them,” said Emilia Palonen, an expert on populism at the University of Helsinki.

“These mainstream parties should be bringing in new issues, new excitement into politics, and instead they’re following.”

Rather than copying the far-right’s emotional appeals toward identity and its criticism of the state, mainstream parties should offer voters fresh alternatives, Berman said.

“[If] center-left parties can’t come up with a better narrative, a better set of policies, a way of making this work, then they are screwed.”