The bloody carnage at a Berlin Christmas market, with a Pakistani or Afghan asylum-seeker as the chief suspect, immediately emboldened right-wing populist critics of Chancellor Angela Merkels liberal refugee policy.
Merkel has been under fire over her decision in September last year to let in tens of thousands fleeing war and poverty from mostly Arab and Muslim nations.
The arrival of around a million people over the past two years has deeply polarised society, and the German leader has said that next year's election would be "more difficult" than any other she has contested.
Hours after the attack that claimed at least 12 lives, Merkel admitted: "I know it will be especially hard for us to take if it is confirmed that the person who committed this attack sought protection and asylum in Germany".
The Islamophobic and anti-immigration populist party AfD wasted no time in laying the blame on Merkel.
"The milieu in which such acts can flourish has been negligently and systematically imported over the past year and a half," the group's co-leader Frauke Petry said in a statement, in a clear reference to Merkel's decision to let in refugees.
"Germany is no longer safe. It should be the responsibility of the chancellor to tell you this. But since she won't do it, then I'll say it," Petry declared, demanding "control over our territory, no ifs and buts".
Marcus Pretzell, also an AfD lawmaker and Petry's partner, went as far as to label the victims of the Christmas market "Merkel's dead".
'Lone wolf or group?'
Merkel's popularity has waned over the record refugee influx, although her decision to seek a fourth term in next year's elections was greeted with approval from 64 percent of the population as measures to curb the refugee influx -- including through a controversial deal with Turkey -- began to show results.
But voters had also punished her over her refugee policy, with her CDU party suffering setbacks in five consecutive state polls, while the upstart AfD saw a stunning rise.
In a world upended by Brexit and the surprise election of Donald Trump, questions are flying on how she plans to counter rising populism.
"Up to now she is the candidate of the conservatives for the chancellor post... but maybe the conservative right-wing will try to get more concessions from her on the questions of internal security and migration," he told AFP.
What emerges from the investigation into the attack could determine how much of a toll it could take on Merkel politically, said Moelling.
A key question was "whether we see that this is a kind of lone wolf approach, or whether there is a more systematic approach or group behind it".
An organised attack would "support the case that we have been unsuccessful in scanning the people coming into Germany last year and it could be seen as Merkel's policy leading to this increased risk," he warned.
For now, most mainstream politicians have been adopting a largely cautious stance.
But Merkel's Bavarian allies, the CSU, who have been among her biggest critics over the refugee issue, are already gearing up for a fight.
"If it's confirmed that this attack was carried out by someone who travelled to this country as an asylum seeker, then in Berlin there should be a fundamental reflection on how this whole refugee reception is organised," Joachim Herrmann, CSU interior minister of Bavaria state, told radio station Antenne Bayern.
He also called for an open dialogue about the risks that Germany is facing due to the arrival of many refugees.
"We need to talk about this question, what risks do we face now with this big number of refugees here," he said in a separate interview with regional radio Bayerische Rundfunk.
But Spiegel Online called for cool heads to prevail, saying "whoever exploits the situation, like the cynics at the AfD are, to incite people against others, is doing the work of terrorists.
"They want to divide us, they want to destabilise use and provoke a cultural war. Their hate is aimed at creating new hate," it warned.