With four weeks to go until the German elections, the current leader in the polls to be the next chancellor, Olaf Scholz from the Social Democrats (SPD), has been put under further pressure over his possible coalition preferences.
Outgoing Chancellor Angela Merkel herself made a rare criticism of Scholz, who is also her current finance minister, over the issue on Tuesday.
She added her voice to what has become a common line of attack against the SPD leader: that he is not ruling out a possible coalition with the hard-left Die Linke (The Left) party.
Merkel's centre-right Christian Democrats (CDU) have rejected the idea of a coalition with Die Linke on the grounds that the party has incompatible foreign policy aims.
Die Linke sees the NATO military alliance - of which Germany is a member - as a relic of the Cold War and describes it as a "war alliance."
The CDU's candidate for chancellor, Armin Laschet, emphasized in Sunday's televised debate that he would not work with Die Linke: "I. Won't. Do. It. Full stop," he said. He has repeatedly demanded a clear answer on the issue from Scholz.
Merkel also weighed in on Tuesday, saying: "With me as chancellor there would never be a coalition in which Die Linke plays a part. And it's not clear whether Olaf Scholz is able to say the same thing... This is a huge difference between me and him [Scholz] when it comes to Germany's future."
Die Linke are polling at around 6 or 7 per cent, and they could help form a majority as part of a left-wing coalition.
Scholz has said that any coalition he leads would have to recognize NATO, but hasn't explicitly ruled out working with Die Linke.
The unflappable SPD candidate's solid campaign has seen his poll numbers rise above Laschet's in the past week, putting huge pressure on the centre-right as they fear losing the chancellorship after Merkel's decade and a half in power.
The Green Party's chancellor candidate, Annalena Baerbock, also distanced herself from Die Linke on Tuesday, pointing to the party's recent refusal to approve the German military evacuation mission in Afghanistan.
The leadership of Die Linke had recommended that its lawmakers abstain in the Bundestag vote. Most did, but some voted for and some against. Die Linke traditionally votes against German military missions abroad.
The Greens would "talk with all democratic parties" after the election. But "Die Linke have ruled themselves out with their vote in the Bundestag," she told reporters in her Potsdam constituency.
