The center-right Christian Democratic Union will elect on Friday a new chairman or chairwoman, who will be the favorite to run for chancellor in Germany's next election. Merkel has been CDU leader since 2000 and chancellor since 2005. She moved her party relentlessly to the center, dropping military conscription, accelerating Germany's exit from nuclear energy, introducing benefits encouraging fathers to look after their young children and allowing the introduction of gay marriage.
Most controversially, she allowed large numbers of asylum-seekers into Germany in 2015. Merkel's popularity lifted her center-right bloc for years, peaking in a 2013 election in which it won 41.5 percent of the vote. But in October, after a troubled start to her fourth-term government and two dismal state election performances, the 64-year-old announced she would step down as CDU leader and wouldn't seek a fifth term as chancellor.
Her potential successors need to lift a party polling under 30 percent. They could take the CDU, which together with the Bavaria-only Christian Social Union has been post-war Germany's most consistently successful political force, in different directions.
ANNEGRET KRAMP-KARRENBAUER, 56 The CDU's general secretary since February, Kramp-Karrenbauer — often called "AKK" — is a Merkel ally and the closest to her centrist stance. She touts her own lengthy experience in regional government, which saw her become the first woman to become a state's interior minister, or top security official, and serve as governor of western Saarland state.
Kramp-Karrenbauer says she knows how to win elections, having defied expectations to win re-election in Saarland by a wide margin last year. And she says she put herself "at the service of the CDU" by giving up that job this year.
Kramp-Karrenbauer has consistently shown more willingness than the chancellor to cater to conservative rhetoric and more vocally opposed gay marriage. Recently, she has sought to put careful distance between herself and Merkel without disavowing her, saying she has had "very lively discussions" with the chancellor on various subjects.
She has talked tough on immigration issues, proposing a lifelong entry ban to Europe for asylum-seekers convicted of serious crimes. But she has warned that endlessly reheating arguments about the 2015 migrant influx is a turn-off for voters.
FRIEDRICH MERZ, 63 A one-time Merkel rival, Merz is seeking a spectacular comeback after more than a decade away from front-line politics. He stands for a more conservative and business-friendly approach.
Merz led the center-right group in parliament from 2000 until 2002, when Merkel pushed him out of that job. He left parliament in 2009, and in recent years practiced as a lawyer and headed the supervisory board of the German branch of investment manager BlackRock.
A snappy speaker, Merz lacks government experience but is well-connected in the party and has presented his time away from politics as a virtue, saying that he has "had the opportunity ... to look from outside at politics and its decisions."
In the past, he advocated radical tax reform and argued that foreigners should learn German "Leitkultur," which could be roughly translated as "majority culture." In this campaign, he has criticized the "unregulated influx" of migrants and charged that the CDU accepted the rise of the far-right Alternative for Germany, which entered the national parliament last year, "with a shrug of the shoulders." He appeared briefly to question the right to asylum enshrined in the German constitution, but quickly walked that back. And he has advocated encouraging greater use of private pension plans using shares.
JENS SPAHN, 38 A Merkel critic, Spahn became health minister in March as Merkel acknowledged pressure for renewal. He has support on the party's right — but that appears to have been largely swallowed by Merz's reemergence, leaving him as the outsider.
Spahn has made migration a focus, calling it the "elephant in the room." He has said that security is a key issue, and argued that "not everything is good again" even though the flow of migrants has slowed.
Spahn, who is openly gay, has said that his party doesn't need to "shift to the right," but it does need to start "a real change of generations." He looks highly unlikely to succeed this time, but this contest could position him well for the CDU's next leadership change.
AND THEN? The choice will be made by 1,001 delegates at a party congress in Hamburg, many of them professional or part-time politicians at federal, regional or local level. Merkel has signaled that she intends to remain chancellor for the rest of this parliamentary term before retiring from politics. The next election theoretically shouldn't be until 2021, but that is uncertain.
Merkel's governing coalition with the center-left Social Democrats, the CDU's traditional rivals, has had an extremely bumpy few months. Another crisis, or an already-agreed midterm review next fall, could bring it down.
Whoever becomes CDU leader will want to follow through on promises to sharpen the party's profile. Observers struggle to imagine Merkel working well with Merz, in particular, though both dismiss that concern.
"I have no doubt that, if that is the outcome, I can work well together with Friedrich Merz, as with every other candidate," Merkel says.