Ever since WW II ended, German elections have generally resulted in a 60-to-80 percent vote with the SPD and CDU/CSU combined:
1972 (Snap Election):
1983 (another snap election):
1990 (another snap election although related to united Germany and expanded Bundestag):
These two center parties have kept a fairly reliable political apparatus in place for over fifty years. In most elections.....they could keep 70-percent or higher of the population within the center core of politics.
So, today? This week, the CDU was noted at 32-percent, the CSU near 8-percent, and the SPD at 21-percent. The federal election is 16 months away, and there is some fear that the CDU and SPD will both lose some points and be near a 50-percent election in 2017.
The shift? People have taken positions on immigration and integration. The core political agenda isn't able to keep half the population happy.
Note: statistical data from Wiki, and one should note that even when the CDU/CSU count was higher than the SPD.....it doesn't mean that they won the election. It's only that they operate as separate entities and in German politics.....the top vote-getter is the controller of the government.