Germany’s Christian Democrats (CDU) will meet to approve a coalition deal with the Social Democrats (SPD) that will take their leader, Angela Merkel, a step closer to a fourth term as chancellor in Europe’s biggest economy.

The last major hurdle to end the five-month political impasse that followed the September election, however, comes next week. On 4 March, the results of a postal vote by SPD members will be announced, and that result is far less certain.

The party conference on Monday follows Merkel’s announcement of her CDU choices for a new, younger cabinet intended to revive the party, which has descended into rows about how to respond to the far-right Alternative für Deutschland (AfD).

Merkel is to address CDU delegates at the meeting before the vote on the deal, which is expected to go through easily.

The conference will also vote on the appointment of her close ally Annegret Kramp-Karrenbauer as CDU general secretary. Dubbed “mini-Merkel” by some media, the 55-year-old Saarland state premier is widely seen as her preferred successor and shares many of Merkel’s views – but not all.

Her Catholic, western German background contrasts with Merkel’s Protestant, eastern roots. While socially conservative – she is known for opposing gay marriage – Kramp-Karrenbauer is a strong supporter of the minimum wage and workers’ rights.

After 12 years as chancellor and almost 18 years in charge of her party, Merkel’s authority is waning and on Sunday she responded to growing calls for new blood at the top of the CDU.

Merkel paid a high price to break the impasse and coax the reluctant SPD back into a loveless “grand coalition”, which has ruled Germany for eight of her 12 years in power.

The deal included the CDU ceding control to the Social Democrats of the powerful finance ministry, seen by conservatives as a guarantor of budgetary rigour in Germany and the eurozone.

Merkel, once the seemingly invincible leader of her party and the nation, has appeared severely weakened in recent months given her protracted struggle to put together a viable coalition for her fourth and possibly final term.

Opponents of her liberal refugee policy have grown more outspoken as the country’s major parties face pressure from the AfD , which has railed against a mass influx of more than a million asylum seekers since 2015.

In a bid to silence critics who want the CDU to shift to the right to win back voters from the AfD, Merkel said she would promote her most outspoken critic, 37-year-old Jens Spahn, to the cabinet.

She said she had carefully chosen a younger team who could bring energy to the job and revive the party’s mood.

After her conservative bloc, which also includes Bavaria’s Christian Social Union (CSU), scored its worst result since 1949 in last year’s election, her efforts to forge a coalition with two other smaller parties collapsed in November.

This forced her to woo the SPD, a reluctant partner, which had seen its own support fall to its lowest since the second world war.

If SPD members reject the deal, the most likely outcome is a new election or possibly a minority government.

Some analysts say the prospect of a new election will spur SPD members into backing the deal to prevent further deterioration in the party’s support. An Emnid poll on Sunday showed the SPD down two points from a week ago, at 17%.