The leading candidate, Friedrich Merz, a conservative who has adopted many of the AfD’s hard-line positions on immigration, used his closing statement of the debate to promise his voters that he would never allow the AfD into his government. Under him, he said, the firewall would hold.

On a wet evening in Suhl, in the former East Germany, a smattering of youthful faces were among hundreds lining up to hear from an unlikely idol - Björn Höcke, one of the most controversial figures in the far-right Alternative for Germany (AfD) party.