Green politicians Tarek Al-Wazir, Priska Hinz and Annalena Baerbock at an election rally in Frankfurt last week. The party is enjoying a surge in popularity in Germany THOMAS LOHNES/OMER MESSINGER

Tarek Al-Wazir, in a suit, immaculate white shirt and thick-rimmed spectacles, looked like a staid Frankfurt banker as he descended the steps into a smoky dungeon nightclub called the Cave.

Yet he didn’t even blink at the sadomasochistic paraphernalia on stage — complete with an X-frame bondage cross — and soon had the crowd cheering.

Al-Wazir, whose father was Yemeni, could become minister-president of the state of Hesse in today’s regional elections, in another shock for the German chancellor, Angela Merkel. As local leader of the Greens, he is riding a wave of enthusiasm for the party that is sweeping through Germany and transforming the political landscape.

Hesse is home to bustling Frankfurt, tranquil spa towns and the forests of Grimm Brothers’ fairy tales. A…