Editor's note: SPIEGEL ONLINE International will be updating its coverage of the German presidential election until a final result is reached after the third round of voting this evening.

Rebels in Chancellor Angela Merkel's coalition dealt her a stinging blow on Wednesday by refusing to back Christian Wulff, her candidate for the post of German president, who failed to secure an absolute majority in the first two rounds of voting in the Federal Assembly.

The vote was billed as a test of Merkel's authority. The large number of rebels in her coalition -- at least 44 in the first round and 29 in the second -- is a strong sign of dissatisfaction in her own ranks after months of in-fighting and setbacks that have led to a slump in popularity

It has heightened speculation that her days as German chancellor may be numbered.

Wulff again got most of the votes for the largely ceremonial post of head of state, with 615 out of 1,238 valid votes. But he fell short of the absolute majority needed to become president. Merkel's coalition of the conservative Christian Democratic Union (CDU), the Bavarian Christian Social Union (CSU) and pro-business Free Democrat Party (FDP) has 644 delegates, which means at least 29 members of that bloc refused to vote for the chancellor's candidate. In the first round the number of rebels was at least 44.

Third Vote Imminent

A third round will be held later on Wednesday in which candidates will no longer need an absolute majority -- more than 50 percent -- to win. They will only need a simple majority -- more votes than their rivals.

The Federal Assembly is made up of delegates from the Bundestag, Germany's federal parliament, and from the 16 regional parliaments.

Wulff's main rival for the presidency, Joachim Gauck, a popular former civil rights activist  from eastern Germany, got 490 votes in the second round, down from 499 in the first. The center-left opposition parties that nominated him, the Social Democratic Party (SPD) and the Greens, together fielded only 460 delegates, which means he managed to attract votes from other parties as well.

At a closed-door meeting after the first vote, Merkel had urged conservative delegates to rally behind Wulff for the second round. "We have common responsibility for the common political goals," she told them.

The glum, deeply concerned faces of Merkel and her allies contrasted with smiles and laughter among opposition politicians. "This means the CDU and FDP are evidently having major problems closing their ranks," said Andrea Nahles, the general secretary of the SPD. "It's positive because delegates are clearly voting for the man they prefer. It shows we have a lively democracy."

A Slide in Popularity

There has been speculation that Merkel's coalition could break apart if Gauck beats Wulff, but it is unclear whether and how that would happen. If Merkel doesn't want to quit, there are major constitutional hurdles that would make it difficult to oust her. Still, it could be the twilight of her term as chancellor.

Wulff, widely regarded as a safe but uninspiring  choice for the post, was nominated by Merkel and her center-right coalition government after the previous incumbent, Horst Köhler, resigned a month ago.

Nominally, Merkel's coalition of conservatives and the pro-business Free Democratic Party command a comfortable majority of 21 in the Federal Assembly.

Opinion polls show a majority of Germans would prefer Gauck, 70, a former Protestant pastor who campaigned  against the East German regime in 1989 before the fall of the Berlin Wall.

Critics said the election has been hijacked by party political interests and that delegates had not been truly free to pick the candidate they really wanted. Several members of Merkel's coalition had said in recent weeks they would prefer Gauck because his personal history gave him a powerful message of freedom and democracy for Germans.

Merkel needs Wulff to win to underscore her leadership following a steep decline in her popularity  since her re-election last September due to acrimonious rifts in her coalition, criticism of her handling of the euro crisis and anger at an €80 billion ($97 billion) austerity program that even some members of her own party regard as socially unjust.