The left-wing Socialist party was endorsed by 21 percent of those sampled by the Insa pollster on January 6-9. The far-left Linke party came fourth with 11 percent.
The migrant-sceptic Alternative for Germany continued to make gains last year and looks set to enter the national parliament for the first time since the party's creation in 2013. It was backed by 15 percent of respondents.
The liberal Free Democratic Party, who teamed up with Merkel’s bloc to rule the country from 2009 to 2013, has been struggling to stay afloat, with just 5.5 percent saying they are ready to vote for it.
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