Here's a look at what's ailing the Christian Democratic Union in the twilight of Merkel's reign.

'Floundering' in the polls?

Although it remains the country's largest political force, recent polls put support for the CDU at 25 percent, just three points ahead of the surging Greens.

The party “is floundering”, the conservative daily Die Welt concluded.

In May's European Parliament elections, the CDU lost more than seven percentage points. It also suffered a black eye in regional elections in three ex-communist eastern German states in recent months, where it faced a fierce challenge from the far-right AfD.

READ ALSO: Far-right AfD second strongest force in Brandenburg and Saxony

The party's decline “can no longer be ignored”, railed senior CDU figure Friedrich Merz, who narrowly lost a bid to become party chief to Merkel's chosen heir, Annegret Kramp-Karrenbauer.

AKK: too many blunders?

Less than a year after replacing Merkel as head of the CDU, the woman best known as AKK is no longer considered a shoo-in to become the next chancellor.

A series of high-profile gaffes have left even loyal Merkel backers wondering if the Catholic mum-of-three is up to the top job.

Newly installed as Germany's defence minister, Kramp-Karrenbauer ruffled feathers when she suggested creating an international security zone in northern Syria, apparently without running the idea past fellow cabinet members first.

A bathroom joke about transgender people during a carnival performance backfired badly, while her clumsy response to a popular YouTuber's criticism of the government's climate policies left her looking out of touch.

READ ALSO: Merkel successor slammed over intersex toilet 

An Infratest Dimap survey this month found that just 19 percent of Germans thought AKK would be a good choice for chancellor, compared to 42 percent for Merz.

But it would be premature to pen AKK's political obituary, said professor Hans Vorländer from the technical university of Dresden. “With time those missteps can fade, allowing her to reassert her authority,” he told AFP.

Congress showdown?

“The question of the chancellorship candidate will overshadow everything else in Leipzig,” Der Spiegel weekly wrote.

The CDU's youth wing has already shattered a taboo by demanding a membership vote on who the party's chancellor candidate should be in the next general election, in a blow to Merkel's succession plan.

Seizing the opportunity, Merz has doubled down on his attacks against Merkel by accusing her of a “lack of leadership”. The corporate lawyer plans to take to the stage in Leipzig right after AKK delivers her speech.

READ ALSO: 'I can win back voters': CDU candidate hoping for Merkel's job

Merkel, who won't seek reelection when her fourth term ends in 2021, will open the annual gathering.

While some in the room may be hostile to AKK, Vorländer said “it was far too early” for Merz to stage a coup.

The party's ambitious health minister Jens Spahn hinted as much when he said last week that the endless leadership debates were “annoying” and that the CDU should focus on governing instead.

Finish line in sight?

Merkel's loveless coalition with the centre-left Social Democrats teetered on the brink last year when a spat over tougher immigration rules sent tempers flaring.

But the alliance between the CDU, their Bavarian CSU sister party and the SPD — reluctantly renewed after 2017's inconclusive general election — now appears on firmer footing after they clinched a hard-fought deal on topping up basic pensions.

READ ALSO: Grundrente: Merkel's coalition reaches deal on Germany's pension reform

A positive half-term review of its achievements also makes it more likely the government will see out the remaining two years of its mandate — and avoid early polls that risk pushing exasperated voters in the arms of the far-right or the Greens.

“The parties in power prefer to stay chained to each other in order to survive,” said Vorländer.

A single regional election next year in the city state of Hamburg will give the coalition partners some breathing room and time to prepare for the post-Merkel era, he added.

Spahn said his party “needs a new team… one that bravely and confidently goes its own way and whose reference point can no longer be Angela Merkel.”