Merkel is a skilled negotiator, renowned at European Union summits for building pressure on her negotiating partners and playing on their fatigue. She must leverage all these skills to secure the three-way "Jamaica" coalition, so-called because the parties' colours match those of the Caribbean country's flag.
"A failure of Jamaica would be her failure," the mass-circulation daily Bild wrote.
Merkel's partner in Germany's previous "grand coalition" - the centre-left Social Democrats (SPD), the second biggest party in the Bundestag (lower house) after the conservative bloc - have said they now want to rehabilitate themselves in opposition after suffering their worst election result since 1933.
Failure to clinch a deal could lead to new elections - a scenario none of the negotiating parties wants for fear the far-right Alternative for Germany (AfD) could make further gains after surging into parliament in the Sept. 24 national vote.
AfD co-leader Alice Weidel criticised the three-way coalition talks for failing to produce results, telling daily Die Welt: "If the (conservative) Union, FDP and Greens don't reach an agreement soon, there should be new elections."
Guenther Oettinger, a Merkel ally and the EU's budget commissioner, told a business conference in Berlin that failure to reach a deal would strengthen far-right populism. "That would hurt us in Europe," he said.
Even if negotiators agree a deal after Thursday's talks, it must still pass muster with lower-ranking party officials.
A key test will be a Greens conference on Nov. 25, when the party's rank-and-file will examine any coalition pact. Despite the challenges facing negotiators, some have no appetite to extend the exploratory talks in the event of no deal overnight.
"If, after three weeks of negotiations, we can't say we can go into a stable governing alliance with each other, then three more days aren't going to help," said Annegret Kramp-Karrenbauer, CDU premier in the western state of Saarland.
