Sounding more like the economics professor he once was than the dangerous far-right firebrand some say he has become, Bernd Lucke spoke at length about the perils of the euro zone and unfettered immigration at a campaign rally last week.

Some 400 conservative, gray-haired men had gathered in a basement of a Hamburg skyscraper on a stormy night to hear the Alternative for Germany (AfD) party founder, a 52-year-old father of five.

Lucke ended his economics lecture and switched into crusading mode: "We won't be blackmailed by a dinky little country with just 2 percent of the euro zone's gross domestic product," he shouted, referring to Greece.

In just two years, Lucke has taken the AfD into the big time -- not with rhetoric or personal charisma, but with an academic approach that reassures his older, conservative audiences.

The AfD entered the European Parliament last May with 7.1 percent, then shocked Germany by winning about 10 percent in three regional elections in the east, stealing voters from Angela Merkel's Christian Democrats (CDU).

The party is now at a crossroads ahead of an election in the city-state of Hamburg next month. If the AfD enters the regional assembly, it would mark its first major success in western Germany, establishing the party as a national force and strengthening Lucke.

Should the AfD fail in Hamburg, the influence of more right-leaning members behind the party's victories in the east and who are flirting with anti-Islam protesters in Dresden, will grow.

"The AfD has been trying to cover a vast range, from those backing liberal economic policies to the national conservative patriots and all the way to the swamps of the far-right," said Thomas Jaeger, a political scientist at Cologne University.

"They've tried to paper over the underlying conflict but that's blowing up in their faces," he said. "It's make or break time for the AfD. Either they'll sort it out or they're doomed."

The AfD power struggle erupted into public view this month.

Lucke wants to change its charter at party congress on Jan. 31, giving the party one leader instead of three. For that, his two co-chairs called him a "despot-style leader". Lucke ally Hans-Olaf Henkel called them "scurrilous".

The AfD tried to defuse the dispute by agreeing to have two leaders from April and one from December. Lucke will face off then against co-chair Frauke Petry, AfD leader in the eastern state of Saxony.

"There aren't any divisions in the party," Lucke told Reuters after a speech that avoided the issue. "Not at all! Where do you get an idea like that?"

LEFTWARD DRIFT

Lucke quit the CDU after 33 years to form the AfD with thousands of CDU defectors put off by its drift leftwards. Moving into that conservative vacuum, the AfD are the first palatable party to the right of the CDU to succeed at the polls.

Germany's Nazi past made it impossible for any half-way respectable far-right party to gain traction before the AfD. It scores 7 percent in opinion polls but pollsters say it could potentially reach 22 percent.

Merkel first ignored and then ostracized the AfD, which draws support from all parties and non-voters. But improving election results have undermined her strategy.

"If they want to remain successful, they need to find a way to unite and keep both wings of the party," a Merkel adviser told Reuters.

Germany's politics are shifting. The Free Democrats, long the CDU's coalition partner, are in disarray after election defeat in 2013. Many FDP voters switched to the AfD, with which the CDU has ruled out a coalition.

On a cold night in Germany's second city, it took a while for the Hamburg crowd to warm to Lucke's warnings of Greece's fiscal mess, euro zone deflation, Germany's low birth rate and the low skill levels of immigrants.

Lucke finally roused the crowd by saying Greece should be thrown out of the euro -- a popular view in Germany -- but predicted Merkel will try to prevent that because it would show the failure of her rescue efforts.

Lucke's lack of charisma may be an asset in a country wary of such things after Hitler.

"Lucke is the antithesis of a charismatic politician," wrote the conservative Frankfurter Allgemeine Sonntagszeitung. "You wouldn't want to go have a beer with him because he's the kind of guy who would order a fanta instead."

One reason why analysts believe the AfD won't quickly self-destruct is that there are experienced CDU veterans in its ranks. Like Alexander Gauland, AfD leader in Brandenburg.

"We believe there should be two wings to this party reflected in the leadership," Gauland told Reuters.

Gauland, born in Communist East Germany but who fled to West Germany and spent 40 years in the CDU, said the AfD thrives in the east because it attracts "conservative, patriotic and -- I mean this cautiously -- nationalist voters."