Germany's new Social Democrat leader, Andrea Nahles, shot to national political fame during the fraught days of the last SPD government 15 years ago when, as a left-wing lawmaker, she helped lead a party rebellion against its tough social reforms.
News that Germany's two biggest parties could soon be headed by women was a welcome kick-off to Germany's carnival season on Thursday, when women storm Rhineland town halls to snip off men's ties and - symbolically - seize power.
Senior figures of Social Democratic Party (SPD), including the current Foreign Minister Sigmar Gabriel, have publicly criticized Schulz and accused him of not keeping his promises. He suggested the SPD had got the better end of the deal, tweeting: "This is the first SPD government led by a CDU chancellor".
Germany's Social Democrats punched above their weight and won.
Under the coalition agreement, the SPD will retain control of the foreign, justice and labour ministries among others.
Germany's coalition deal must win support of SPD party members or risk falling apart.More news: Justin Timberlake brings 'SelfieKid' to tears with surprise call, show tickets
But before anyone can take up their posts in a new Merkel-led cabinet, the SPD's rank-and-file have to give their blessing to the coalition pact.
CDU members are smarting at having to cede the vital Finance Ministry to the SPD. "What's left is regret at how little respect there is in the Social Democratic Party in our dealings with one another, and how little someone's word counts for", Gabriel told the Funke newspaper group.
Former European Parliament chief Schulz said he meant to take over the foreign ministry and was giving up the SPD leadership after just over a year in the role. Gabriel himself surrendered the party chairmanship to Schulz in January 2017.
The result of the SPD vote is expected to be announced on 4 March, with CDU delegates also getting a chance to vote on the coalition deal at a party congress on 24 February.
Schulz's candidacy initially boosted the Social Democrats in the polls.
Second, members realise a rejection of the proposed coalition would leave the party without an easy "exit option" - new elections would likely see the SPD score even worse than the record low 20.5% it secured previous year, polls putting it around the 17% mark.
Merkel has relied on exactly this coalition for two of her three four-year terms.