By Thomas Escritt
ERFURT, Germany (Reuters) - The convention by which Germany's far right is kept far from government regardless of how many parliamentary seats it wins was dealt another blow on Thursday when its votes were used to defeat a regional government in a crucial budget bill.
The far-right Alternative for Germany (AfD) party has been leading in polls in parts of eastern Germany for months, benefiting from dismay at rising prices and uncertain economic prospects, but a so-called "firewall" of all other parties joining together has kept it far from power.
Thursday's vote in Thuringia's parliament, when the far right, the conservative Christian Democrats and the pro-business Free Democrats combined to push through a tax cut against the wishes of the left-wing coalition, is the latest sign of change.
"This is the blackest day of my long parliamentary career," said Thuringia's premier Bodo Ramelow, saying the CDU could have consulted with his coalition on a way of delivering on their goal of helping the poor without voting with the AfD.
But, highlighting the dilemma, the regional CDU leader Mario Voigt said such a course of action would effectively deprive him of the right to oppose.
"I can't make good, important decisions that help families and the economy, subordinate to the risk that the wrong people might vote for them," he said.
Last month, the Thuringian district of Sonneberg elected Germany's first ever AfD district administrator, while in the state of Saxony-Anhalt the AfD's administrator candidate came first and will now face off against the second-placed candidate in a run-off.
The party stands at 32% in the polls in Thuringia, and also tops the polls in three other states of the former East Germany, where allegiances to the parties inherited from West Germany are weaker and where lower incomes make the economics hurt more.
But it is in the rolling hillsides of thickly forested Thuringia that the AfD's success rings the most alarm bells: anti-terror authorities there are formally monitoring the regional organisation, which they deem extremist.
The party's regional leader, Bjorn Hoecke, is currently on trial for hate speech after uttering a slogan that stems from a Nazi chant.
The party is part of a "mosaic" of far-right organisations that has taken root in the state, taking advantage of cheap real estate and motorways that can rapidly get them anywhere in Germany, said Thuringia's security service head, Stephan Kramer.
But the party's polling performance, which most recently saw the AfD becoming the most popular party in the state of Brandenburg that surrounds Berlin, leaves many doubting that the cordon sanitaire can last.
"We democrats have a common responsibility to oppose the AfD," Daniel Guenther, premier of the northern state of Schlweswig-Holstein, told the Frankfurter Allgemeine.
"We democrats have to stop the finger-pointing, sit down together and find a position that lives up to that responsibility."
(Reporting by Thomas Escritt, Editing by Rachel More and Nick Macfie)