The leader of Germany's far-right AFD party in Thuringia state is Björn Höcke, a right-wing populist who has been called a Nazi by opponents.
AFD is forecast to get about 23% of the vote in elections in the east-central state on Sunday, a 10% gain on the last time out.
Last month the party made big gains in two other regional elections in former communist East Germany.
Chancellor Angela Merkel's Christian Democrats are expected to win. Its candidate, Mike Mohring, has publicly called Höcke a Nazi.
A coalition is currently in power consisting of the Social Democrats, the Greens and led by state president Bodo Ramelow.
It's the first state to be ruled by the left since Germany reunified in 1990.
Controversially the intelligence services illegally opened a file on him for links with the communist party in the 1990s.
But now the SPD is expected to lose around 9% of the vote, which could make it difficult for Ramelow to form another coalition.
Meanwhile, Hocke's campaign in Thuringia has been trying to recreate the spirit of the protests in old Communist East Germany that led to the fall of the Berlin Wall 30 years ago.
But even Hocke's fellow AFD party leaders in western Germany are distancing themselves from his extreme right-wing rhetoric.