From Opinion polling for the German federal election, 2017, poll were quite stable between 2014 and 2017, only with a gradual decline of CDU/CSU with a moderate rise by AfD since late 2015¹:
Source: Wikimedia Commons.
However, since the beginning of 2017, the SPD has risen dramatically, seemingly at the expense of all other parties except FDP. CDU/CSU had a virtual 15-percentagepoint lead that has essentially vanished. The SPD situation is in contrast with the situation of social-democratic parties in other northern/western European countries such as France, UK, or The Netherlands, where social-democratic parties are doing poorly in polls or in reality. In neighbouring The Netherlands, where social-democrats are the junior party in a grand coalition similar to the one in Germany, social-democrats have consistently polled below 15% since 2013 and below 10% since 2015 and are now the 7th party, polling at 7.4–8.5%.
What are the causes of the sudden recent increase in the opinion polls for the SPD?
¹Around ⅛-⅐ of CDU/CSU-voters apparently moved to AfD, this is often attributed to dissatisfaction over the refugee policy, EU, and Euro.