By Sarah Marsh and Andreas Rinke
BERLIN (Reuters) - Germany's new leftist populist party aims to exact a high price from mainstream parties for helping them govern three eastern states: demanding that their regional officials join calls to stop arming Ukraine.
Such concessions risk eroding the pro-Ukraine consensus in Germany, Kyiv's second biggest military supporter against Russia's full-scale invasion of its neighbour. They are also fostering tensions in Chancellor Olaf Scholz's three-way federal coalition in Berlin, which is already hanging by a thread.
Launched in January, the Sahra Wagenknecht Alliance (BSW) is the only party to oppose arming Ukraine besides the far-right AfD, a pariah because other parties refuse to work with it.
The BSW's electoral successes in the states of Brandenburg, Thuringia and Saxony in September make it a near-indispensable partner for mainstream parties seeking to form coalitions there.
Sahra Wagenknecht, the popular but divisive leader after whom the Russia-friendly, NATO-sceptic party is named, wants its regional branches to force any potential partners to sign up to its anti-war positions as the price of a coalition.
That led this week to the Brandenburg branch of Scholz's Social Democrats (SPD) endorsing a joint statement with the BSW which included the message: "The war will not be ended by further weapons deliveries."
The text, which also criticised the possible deployment of U.S. long-range missiles in Germany, sparked outrage in Berlin and disquiet among some within the SPD.
Agnieszka Brugger, senior lawmaker for the Greens - junior partner in Scholz's government - accused the SPD of kowtowing to the BSW's "cynical and populist course".
"Anyone who talks about peace but means an end to support for Ukraine does not want real peace," she told Reuters. "Such a policy would jeopardise the security of our country and our allies."
The SPD mayor of Munich, Dieter Reiter, said the Brandenburg party's language was "unacceptable".
While Germany's state governments have no direct influence over foreign policy, the BSW's stance comes as some surveys show public opinion already cooling on support for Ukraine at a critical time - with Russia making battlefield advances and U.S. policy on Ukraine dependent on the Nov. 5 U.S. election.
The BSW's manoeuvres are also strengthening the SPD's traditionally Russophile left flank, said Stefan Marschall, political scientist at the University of Duesseldorf.
The SPD last month appointed as General Secretary leftist Matthias Miersch who appears to be rehabilitating Gerhard Schroeder, the former chancellor who worked for Russian state oil company Gazprom (MCX:GAZP) and calls President Vladimir Putin a friend.
RISK OF IMPLOSION
Blending paternalistic economic policies with an anti-migration stance, the BSW scored double-digit results in all three states in September and is on track to win 7-9% at the federal election next year, according to polls.
That has turned the cerebral Wagenknecht, 55 - who started out as a Leninist theoretician for the old East German Communist party - from a cult figure of marginal political importance to talkshow staple.
But there are signs that her demands on local party barons are already straining the limits of her authority, in turn testing the young party's cohesion.
In Thuringia, regional BSW leader Katja Wolf, a popular former mayor of Eisenach, was content in coalition talks with the SPD and the conservatives to relegate talk of peace and war to a vaguely worded, non-binding preamble.
For Wolf, who said she had joined the new party out of alarm at the far-right's success in her state, building a stable government was the priority.
Wolf earned a stern rebuke from party headquarters who demanded a more “recognisable BSW signature” in the agreement.
Critics say Wagenknecht would rather forgo regional power than dilute her message ahead of the bigger prize of the national election.
Wagenknecht has a bad track record of sustaining political movements and the BSW could yet implode, said political scientist Oliver Lembcke at the University of Bochum.
The "Rise Up" initiative she launched in 2018 petered out within a year. Wagenknecht said at the time that she left the movement due to burnout.