The German capital, one of the country's 16 federal states, has been ordered by the courts to return to the ballot boxes as the last vote on September 26, 2021, failed to meet basic democratic standards.
Opinion polls in the run-up to the election put the CDU conservative opposition in pole position, ahead of Scholz's SPD, who came first in 2021.
If the trend is confirmed, it would mark the first time in over 20 years that the CDU has topped the regional vote in the capital.
SPD general secretary Kevin Kuehnert underlined the impact of the local vote on a national level, warning that it could determine whether Scholz continued to have strong SPD-led states behind him as he seeks to implement his plans for Germany.
Any upset risks shifting the balance of power in the Bundesrat, the upper house of the federal parliament, which represents the regional states.
"A lot has changed since" the vote in 2021, making for an unusual contest, said Thorsten Faas, professor in political science at Berlin's Freie Universitaet.
The Russian invasion of Ukraine has shifted the political landscape and the timing of Sunday's vote -- no longer falling on the same day as federal elections -- means turnout will likely be lower, he told AFP.
'Difficult and challenging'
The rerun in Berlin is only the second time in German post-war history that a state election has been declared invalid, after irregularities were reported in a vote in Hamburg in 1991.
Incumbent Mayor Franziska Giffey, who leads a fractious coalition between the SPD, the Greens and the far-left Die Linke, has described the ordered repeat vote as a "difficult and challenging situation, particularly in the current crisis" with soaring energy prices in the wake of the Ukraine war.
Opposition parties have made hay with the electoral debacle, as well as an outcry surrounding violent clashes during New Year's celebrations in the city and tussles over transport policy.
CDU challenger Kai Wegner might claim a mandate to lead a coalition government in the city, if his party comes top with 25-26 percent of the votes as suggested by opinion polls.
The balance of power in the Berlin Senate after the vote however could still be in Giffey's favour, offering her an easier way to remain mayor by marshalling current partners.
But the Social Democrat has insisted that she is campaigning for the "SPD to remain the strongest political force in this city".
Marathon vote
The organisation of the 2021 election on the same day as a national vote, a local housing referendum and the Berlin marathon had led to widespread logistical problems.
Ballot papers got stuck in traffic as roads were closed for the race, with lines forming outside polling stations struggling to process votes.
Federal election officials found voting irregularities in Berlin districts equivalent to about half the city.
The German parliament has also resolved for national elections to be partly repeated in Berlin, with the date of that vote yet to be set.
The 2021 fiasco is a further stain on the reputation of the capital, where administrative snags are commonplace.
Sunday's election will take place under the watchful gaze of international election observers from the Council of Europe, invited in by the city itself to restore trust.
Berlin has also called up an army of 42,000 election helpers -- 8,000 more than last time around -- and plans to give polling stations extra ballots to avoid shortages.
Comments