"It's a surprisingly sharp decline," political scientist Andreas Johansson Heinö told the TT newswire.
The Sweden Democrats were widely expected to hang on to their position as Sweden's second-largest party after the Social Democrats. But on election night the party slipped by three percentage points and lost voters in all but five municipalities.
"What makes this particularly noteworthy is that the three government parties made gains while the Sweden Democrats lost ground. I think few people expected that," said Johansson Heinö, a political scientist and publisher at the free market think thank Timbro.
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"It sends a clear signal from the electorate. More voters appreciated the approach and policies of the three centre-right government parties on key issues."
On election night, party leader Jimmie Åkesson explained the outcome by arguing that the Sweden Democrats had fought hard for the governing Tidö coalition, causing more voters to support the coalition as a whole rather than a single party – and ultimately turning to the Liberals on election day.
Johansson Heinö said he viewed Åkesson's analysis as an attempt to put a positive spin on the outcome.
"Voters know what they are doing, whether they vote for the Sweden Democrats or not."
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Support also appears to be falling among young people. In Sweden's mock school elections, where the Moderate Party emerged as the largest, the Sweden Democrats suffered the steepest drop, falling by seven percentage points.
"There is still a right-wing wave among young voters, but the Moderates have managed to outcompete the Sweden Democrats to some extent," Johansson Heinö noted.
Hällefors in the Örebro region saw the Sweden Democrats suffer its biggest losses. A plausible explanation is that the upstart Örebro Party, led by far-right demagogue Marcus Allard, poached Sweden Democrat votes. Although far-right challenger parties such as the Örebro Party, Alternative for Sweden and Medborgerlig Samling remain small, those votes can make a significant difference when election results are tight.
"While the Left Party, for instance, seems to have successfully neutralised the Nyans party – which was seen as a threat in many constituencies – the Sweden Democrats haven't quite managed to curb competition on their own flank," said Johansson Heinö.
"Those who believe the Sweden Democrats should have been more radical will certainly argue that there wouldn't have been room for these alternative parties if the Sweden Democrats had maintained a harder edge."
Conversely, others are likely to point out that it is precisely the radical rhetoric – such as high-profile Sweden Democrat MP Richard Jomshof's controversial remarks about treason and Muslims – that repels voters.
"I think a good number of voters feel they went too far there," said Johansson Heinö.
A three-point drop is by no means a total collapse. The Sweden Democrats remain a major political force that grew rapidly from an outcast fringe party into a mainstay of government offices.
But with that expansion comes a more fickle voter base.
"The bigger you get, the harder it is to rely solely on core supporters. In that sense, a drop in support is a completely normal development," said Johansson Heinö.
"It's just that the Sweden Democrats haven't experienced this before."