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 Sunday, the country’s residents will vote in a pivotal election in which Ms Weidel's party, Alternative for Germany (AfD), is tipped to come in second. A snap election was called at the end of last year by current Chancellor Olaf Scholz, of the Social Democratic Party (SPD), when his coalition Government fell apart.