The Social Democrats' decision on Monday to nominate political professor Gesine Schwan to challenge conservative President Horst Köhler in Germany's presidential election next May has angered Chancellor Angela Merkel's Christian Democrats (CDU) and rammed another nail in the coffin of their grand coalition government, write German media commentators.

But Merkel's left-right government is unlikely to fall because neither party will dare to withdraw from the coalition and risk being blamed for its collapse. Both the Social Democrats (SPD) and the CDU know that German voters would punish the perceived culprit at the ballot box. Nevertheless, this government is now too weak and divided to take any major decisions in the remaining 16 months of its term, say commentators.

Meanwhile, few believe SPD leader Kurt Beck's promise that his party won't cooperate with the Left Party after the general election. Schwan's nomination is widely seen as the first step towards an alliance between SPD and the Left Party, vilified by the conservatives because of its roots in the communist party that ruled East Germany. SPD member Schwan, 65, held in high regard in the SPD for her eloquence, self-confidence and infectious enthusiasm for political debate, will need votes from Left Party members of parliament to get elected in the May 2009 vote for the presidency, which is a largely ceremonial, apolitical position. That, say some commentators, is bound to herald some form of "red-red" cooperation between the SPD and the Left Party after the general election four months later.

Former SPD leader Franz Müntefering urged his party to strictly rule out such an alliance and took a swipe at both Beck and Merkel in an opinion piece published in the Süddeutsche Zeitung newspaper on Tuesday in which he said: "The political leadership of our country is largely vacant."

The left-wing Die Tageszeitung writes:

"The coalition crisis will remain absurd because neither the conservatives nor the SPD will dare to break it up. After all, they haven't got any alternative coalition partners, and an early election can be ruled out because it would undermine the credibility of both parties if they dissolved parliament prematurely yet again."

"But this grand coalition won't be taking any more major decisions. Or put another way: this government has turned into a non-government organization, with immediate effect. The election campaign has begun, 16 months before the general election."

"The conservatives can only interpret this candidacy of Gesine Schwan against incumbent Horst Köhler as meaning one thing: The red-red camp of the SPD and Left Party is starting to form itself."

"The grand coalition was no successful model for Germany, and Schwan's nomination shows that the SPD has understood that."

The Financial Times Deutschland writes:

"It cannot be denied that the SPD is opening the door to the Left Party yet a little bit wider. The Left Party's votes have been factored into the 'Schwan for President' project."

"At the moment the SPD's assurance that it won't cooperate with the Left Party at the national level only means that it won't cooperate in parliament. But different rules apparently apply a few hundred meters away, in the president's Bellevue Palace in Berlin. The SPD will have to live with the fact that people are going to have their doubts in this respect."

The center-left Süddeutsche Zeitung writes:

"The conservatives can be expected to wage a campaign accusing the SPD of cooperating with 'communists'. One can scarcely describe it as cooperation if a party supports the candidate of another party, but the conservatives will demonize it as the harbinger of cooperation between the SPD and Left Party. Whether this demonization works will be the most exciting aspect of the months to come, and the outcome will have an impact on future political debate."

The conservative Frankfurter Allgemeine Zeitung writes:

"The SPD is limiting its options with Schwan's candidacy. It won't be making the (business-friendly) Free Democrat Party, which regards Köhler as its man, any keener on entering into a coalition government with it in the future. And relations with the conservatives are now totally poisoned. So after the next general election the only remaining option for the SPD is the one it is now completely ruling out, even though some of its own members are preparing it step by step."

The mass-circulation Bild writes:

"This is highly risky for the SPD and its leader Kurt Beck. Who's going to believe the party when its officials claim that it won't embrace (Left Party leader) Oskar Lafontaine  after the next general election, if the SPD and Left Party jointly back Schwan in the presidential election four months before that?"