After weeks of bitter infighting, co-leader Frauke Petry made the shock announcement this week that she would not seek to lead the AfD's campaign at the gathering starting Saturday in the western city of Cologne.
The news left the upstart anti-immigration party reeling and set the stage for a showdown between populist and more radical, hard-right forces.
"(Petry) has been unable to stop the AfD, which began as a party of euro critics, from becoming more and more a catch-all for racists, right-wing nationalists and the far right," Cologne's daily Stadt-Anzeiger said.
"The fight within the AfD rages on."
Founded in 2013 on a eurosceptic platform, the AfD has railed against Chancellor Angela Merkel's decision to let in more than one million asylum seekers to Germany since 2015.
But its fortunes have declined as the number of new arrivals has dwindled, and all of Germany's mainstream parties have ruled out working with it should it clear the five-percent hurdle to representation in the September 24 election.
Opinion polls show the AfD at between seven and 11 percent, a steep drop from the 15 percent support it drew only late last year.
Merkel is seeking a fourth term after nearly 12 years in power and her conservative Christian Democrats are currently leading the polls.
But the AfD claims credit for helping to push her to toughen Germany's border policy in the wake of the refugee influx.
And AfD seats in the Bundestag lower house -- a first in Germany -- would complicate the process of forming a ruling coalition for Merkel or her main challenger, Martin Schulz.
'Tearing itself apart'
Authorities are bracing for a massive counterprotest of around 50,000 people and have set up a broad security zone around the congress venue, a hotel in the city centre.
"We have information that several thousand left-wing extremists will be coming to Cologne... including several hundred violent people," police chief Juergen Mathias said.
The telegenic Petry, a 41-year-old trained chemist who is pregnant with her fifth child, has aligned herself with kindred spirits across Europe, including far-right firebrand Marine Le Pen, one of the frontrunners for the first round of French elections Sunday.
But given the long shadow still cast by Germany's Nazi past, Petry has argued the AfD must make itself more palatable with a more moderate-sounding "middle-class" platform she will put to a vote at the congress.
The stated goal is to become Germany's ruling party by 2021.
Denouncing "provocations" by party officials, Petry has called for the ouster of an AfD state leader, Bjoern Hoecke, who in January sparked outrage by slamming Berlin's vast Holocaust memorial as a "monument of shame".
Although Hoecke has been barred from attending the congress, some delegates have said they will put forward a motion to keep him in the party.
Petry's chief rival, 76-year-old Alexander Gauland, a hardline defector from Merkel's CDU, has said he would back the initiative.
Analysts say the vast majority of the AfD's core supporters are far to the right of the political spectrum.
However they say there is little appetite among most German voters for radical change, particularly after the victories of Donald Trump in the United States and the Brexit camp in Britain.
"In terms of its voters, Petry's attempt to make the AfD a middle-class mainstream party is a very unrealistic strategy," Robert Vehrkamp of the Bertelsmann Foundation think tank told Spiegel Online.
The news website said the party's inner turmoil also diminished the threat it posed to the establishment in Europe's top economy.
"While in the rest of Europe, opponents of immigration and the EU are on the march, the AfD is busy tearing itself apart," it said.
"That is good news for the traditional parties and the defenders of liberal values in Germany -- at least in its current state, no one needs to fear the AfD."
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