Merkel still looks set to secure a third term in Sunday’s general election.
But the Alternative for Germany (AfD), which has risen on a tide of public hostility to bailouts of indebted southern eurozone countries, could further fragment the lower house, forcing her into a right-left “grand coalition”.
A breakthrough for the party, which advocates forcing weaker members out of the single currency area, would send shock waves around Europe and could spook financial markets, even though its voice in parliament would be small.
An INSA poll gave Merkel’s conservatives 38% and their liberal Free Democrat (FDP) allies 6%, putting the centre-right one point behind the three left- of-centre opposition parties, with a combined 45%.
The survey was the first to show the AfD, created just seven months ago, clearing the 5% hurdle to win seats in the Bundestag lower house. Its best score in other polls has been 4%, but pollsters say it may have higher unavowed support.
If the AfD becomes the first new party to enter the Bundestag since 1990, Merkel would probably have to negotiate a coalition with the pro-European opposition Social Democrats (SPD), with whom she governed in 2005-2009.
The ruling Christian Democrats (CDU) had tried to ignore the AfD, but abruptly changed tack this week and deployed respected finance minister Wolfgang Schaeuble to attack the sceptics, who want Greece and other bailout recipients out of the euro.
The 71-year-old minister, a veteran supporter of European integration, said the AfD’s anti-euro argument “has no credibility and is extremely dangerous for our prosperity”.
Led by university professors and supported, in the words of one pollster, by “grumpy old men”, the AfD is mopping up right- wing protest votes and some of the millions who could not be bothered to cast ballots in 2009.
“The interesting thing is that 41% of AfD voters either voted for the ‘other parties’ category or not at all in 2009,” said INSA chief Hermann Binkert.
Most other AfD supporters said they had voted centre-right last time but 9% came from the hard Left, also critical of the euro, and a handful from the SPD and Greens.
Merkel and the AfD have ruled out working with each other in the Bundestag, but one CDU leader — Volker Bouffier, who defends his premiership of Hesse in a state vote on Sunday — said he might consider it, before retracting after a storm of criticism.