The approaching election in Sweden has been variously described as “the most important election of this century”, “the election of a lifetime” and “a must-vote election”. Why the hype? Because the stability of the entire Swedish party system is threatened with collapse.

The agent of this potentially radical change is a new party that refuses to fit into the traditional centre-left vs centre-right blocs that dominate Swedish politics.

By making anti-immigration their core issue, the Sweden Democrats have carved a niche for themselves that is best described as “welfare chauvinism”. The party has crafted a message that combines cultural conservatism with an interventionist state. It leans to the right on traditional values, morality and identity but to the left when it comes to welfare spending.

Many members have made discriminatory remarks and promoted xenophobic attitudes. For this reason, until this point, mainstream parties have been unwilling to associate themselves with SD.

Now the Sweden Democrats are likely to win their largest ever share of the vote in the election on September 9 – that’s anywhere between 17% and 21%. The main opposition, the centre-right Alliance coalition, can count on about 38%, and the ruling coalition between the Social Democrats and Green party around 39%.

If these projections play out, no bloc will win a majority large enough to govern alone. And negotiating a stable coalition government will be very difficult.

Sweden Democrats entered the national parliament for the first time in 2010, winning 20 seats. In 2014, they surged again, taking 49 seats in the Riksdag to become the country’s third largest party.

This is quite a feat for a party grown out of neo-Nazi, radical right-wing roots – and Jimmie Åkesson, party leader since 2005, must take the credit. Under his direction, the party dropped the extreme rhetoric, and moved more to the centre of the political spectrum, while remaining strongly attached to nativist ideals. In 2018, the SD party agenda includes a sharpening of immigration, family reunification and citizenship rules, higher spending on healthcare, and the promise of a referendum on Sweden’s membership of the European Union.

Sweden Democrats also seem to be benefiting greatly from the work of an army of Twitter bots in this election. A recent study by the Swedish Defense Research Institute found that 2,618 automated Twitter accounts were sending 6% of the content bearing the hashtags #svpol and #val2018 gathered since March 2018. Almost half of the messages broadcast by these bots sympathise with the Sweden Democrats. Many were attacking SD’s opponents: 42% were directed against the Social Democrats.

The nativist discourse of the Sweden Democrats has also provoked a strong counter-reaction. Left-wing grassroots organisations have protested against the party’s message, sometimes culminating in violent confrontations. Public figures have signed letters criticising the party. Hotels and conference centres have refused to house Sweden Democrats meetings for fear of putting off other customers. These incidents are testament to the deep polarising effect the party is having in Sweden.

There are basically only three options on the table in this election: a minority coalition government by either of the two blocs, with informal support in the parliament from the other parties; a cross-ideological grand coalition between the left and the right; or a coalition government between either of the two mainstream blocs and the Sweden Democrats.

The latter remains an improbable scenario. All mainstream parties are still nominally committed to their cordon sanitaire policy towards Sweden Democrats. This does not mean, however, that the disruptive power of the Sweden Democrats will not be felt.

Any minority government will be very weak and inclined to make unsustainable compromises just to pass policies through parliament. In a grand coalition scenario, all ideological differences will be swept under the carpet, including on the subject of immigration and integration. This will likely result in an increase in support for the anti-immigration manifesto of the Sweden Democrats. So even without a formal place in the government, the upstarts will make their presence felt.

On top of the political uncertainty, the rise of the Sweden Democrats is already being felt in the national economy. Investors and businesses are wary of the unsettling period that will follow the elections and appear to be hanging back from making deals. The influence of a party that is so critical of globalisation and favours “Swexit” is causing jitters.

Instability and polarisation are unwanted developments for any society, because they reduce the governing capacity of the state and create social tensions. Should there be any positive consequence of the surge in Sweden Democrats’ support it lies with how the mainstream parties meet the challenge. The best hope is that they do so by providing better solutions to the problems signalled by the popularity of this disruptive newcomer.