Angela Merkel faces a tough election challenge from the wildly popular Martin Schulz

German Chancellor Angela Merkel faces a tough fight to keep her job after the country’s center-left party voted for Martin Schulz – a popular, straight-talking, and stridently anti-populist politician – to challenge her at elections in September.

At a conference in Berlin Sunday, Germany’s Social Democrats (SPD) voted unanimously for Schulz as their new leader – an unprecedented action in the party’s post-war history.

His selection was no surprise. Since Schulz, a former president of the European Parliament, announced his intention in January to contest the leadership, his party has surged 10 points in the polls to draw nearly level with Merkel’s Christian Democratic Union (CDU), and 13,000 new members have signed up at a time when the fortunes of Europe’s social democratic parties are generally on the decline.

“This is an overwhelming moment for me and for us all,” Schulz said during his victory speech, in which he pledged to support working people, fight for social justice, and combat a wave of populism and anti–European Union sentiment currently jolting the continent.

The SPD’s remarkable poll boost is directly attributable to Schulz, a straight-shooting new face in German domestic politics who has been “positioning himself as the antithesis to populism,” Nina Schick, a German political commentator, told VICE News.

“He uses things like Brexit and Trump’s election to say: I stand for the opposite of that, I stand for social democratic values,” she said. In his remarks Sunday, Schulz denounced the U.S. president’s “misogynistic, anti-democratic, and racist” speech, and pledged to defend the European Union.

The SPD, currently the junior partner in a “grand coalition” with Merkel’s CDU, has been seen as drifting away from its roots in recent years, struggling to differentiate itself from its senior partner.

“He’s trying to take it back to its roots as a party working toward a society that works for everyone,” Schick said. Schulz has blamed growing inequality for the rise of populism, and has slammed CDU plans to cut welfare programs and boost spending on defense.

Schulz’s appeal is helped by his reputation as “a tough-talking, no-bullshit man of the people.” An aspiring football player in his youth who became an alcoholic after being injured (he’s since cleaned up), he ran a bookshop for years before forging a career in politics. His strong European credentials – he is viewed as being even more pro-EU than Merkel – were another strong draw for young voters, for whom defending the European project is shaping up as a critical issue, said Schick.

But at a time when the country is widely considered to be faring well, stopping Merkel from winning a fourth term in office will be an uphill battle. With little separating Merkel and Schulz on key issues such as the E.U. and Germany’s refugee policy, the campaign is likely to hinge on nuances in their argument, or public desire for a fresh face after 12 years with Merkel in charge, Schick said.

On current polling, the SPD would have no option but to build a coalition with left-wing parties if it wanted to lead the next government. A return to a grand coalition with Merkel’s CDU was another option, but the SPD could be reluctant to do so again, posits Schick.

“Having done that recently, they feel that Merkel has been good at taking their flagship policies and making them her own,” she said. “They can’t differentiate themselves, and that could be a death spiral for them.”

After her “open door” policy toward refugees proved a political liability, Merkel tacked to the right on the issue. It remains to be seen what moves she has in store to respond to this latest and most serious challenge to her bid for a fourth term.