BERLIN — Nontraditional and upstart political parties are threatening established, centrist parties across Europe, as returns from the European Parliament election underscored this week. Their rise is eating away at an increasingly endangered political establishment.

Adding to the uncertainty is a generational divide clearly visible in the voting, in which the Greens drew significant support from younger voters.

Germany is no exception.

A national election is not scheduled until 2021, and Chancellor Angela Merkel has said she intends to serve out her full term. But in the aftermath of the European vote, the two parties in Germany’s governing coalition are frustrated and weakened, and speculation is rising over how long their unpopular government can last.

Support for both the chancellor’s conservative party and its center-left partners declined in the election. The chancellor’s party, the Christian Democrats, lost five seats, earning only 28.9 percent of the vote. Their partners, the Social Democrats, endured their worst national showing ever, with support from only 15.8 percent of the voters.