A coalition between Merkel’s CDU/CSU alliance – which lost ground to the AfD in September’s ballot – and the SPD has governed Germany for eight of the last 12 years.
But it has tended to be viewed as a last resort by both politicians and voters as it leaves the opposition weak.
A poll for broadcaster ARD showed more than half of the electorate – 52 percent – are sceptical about reviving it, while 45 percent are in favour.
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Not natural allies, the two camps are likely to clash on immigration, tax, healthcare and Europe – and expectations among other leading figures in the parties were mixed as the preliminary talks got under way.
Norbert Roemer, SPD head in the regional assembly of North Rhine-Westphalia, told the RND newspaper group no lawmakers in his state caucus favoured a grand coalition – unlike five years ago – with past experience meaning they no longer trusted Merkel.
Volker Bouffier, a senior member of Merkel’s Christian Democrats (CDU), told Rheinische Post newspaper his party intended to form a grand coalition but that it could not come at any price.
Horst Seehofer, leader of the Christian Social Union (CSU) – the Bavarian sister party to Merkel’s CDU – said he was going into the talks in “high spirits” and participants needed to come to an agreement.
The potential partners have agreed on a news blackout during the exploratory talks, which are due to finish on Thursday.
If they find enough common ground and the SPD gets backing from its members in a vote, the parties will proceed to full-blown coalition talks. The consensus among politicians and observers expect those would last until at least March.
But if the discussions fail, Germany could either face fresh elections or, for the first time in the post-war era, a minority government run by Merkel.