Speaking to Bild over the weekend, Gabriel explained that Steinmeier is the best candidate for the post of head of state, since he knows how to represent the country and has the answers "to the challenges of our time."
"Neither the Christian Democratic Union, nor any other party has nominated a candidate who could be even remotely compared to Steinmeier," Gabriel said, referring to the party of Chancellor Angela Merkel, with which the SPD is part of the current grand coalition government.
Under German law, the president is selected by the Federal Assembly for a five year term. In practice, none of the countries' major parties has enough votes to push their favored candidate through without the approval of other parties.
The search for a new head of state has been further complicated by the fact that Germany is set to hold federal parliamentary elections next fall. Experts say that while the election campaign has not formally begun, it is de facto already under way, resulting in an uncompromising mood among politicians, including as far as presidential nominees are concerned.
Accordingly, despite Steinmeier's national popularity, Gabriel and the Social Democrats understand that electing the politician president will be impossible without the support of Merkel's center-right bloc, including the CDU and Horst Seehofer's Bavarian Christian Social Union.
Last month, Russian political scientists suggested that Merkel and her party might actually do well to approve Steinmeier's candidacy, given his present status as the most popular politician in the country, with an approval rating of 75%. With Merkel's approval hovering just over 50% and continuing to slide, approving Steinmeier as president may take him out of the running as a candidate for chancellor next October.
Gabriel visited Moscow last month for two days of trade talks. A consistent critic of anti-Russian policy, the politician has promoted a policy of looking for 'points of convergence' with Moscow, including economic cooperation.
Steinmeier too has voiced opposition to anti-Russian policy, including the recent proposal to level new sanctions against Moscow amid the situation in Syria's Aleppo. A proponent of the Minsk agreements on restoring peace to eastern Ukraine, which he personally helped to broker, Steinmeier recently indicated that he was frustrated by the fact that the deal's implementation has progressed "at a snail's pace." Kiev has been accused of refusing to adhere to the peace plan by insisting that its thirteen points can be implemented out of the order they were agreed to, an idea that leaders of the fledgling Donbass republics have rejected.
Recently, Steinmeier warned that unless the European Union focuses on its internal problems, including the "violent turmoil" caused by the Eurozone's financial crisis, the influx of refugees and shocks caused by the UK's Brexit referendum, the union itself might face collapse.
Other possible contenders for the German presidency include Finance Minister Wolfgang Schauble, Bundestag Speaker Norbert Lammert, Defense Minister Ursula von der Leyen, CSU parliamentary group leader Gerda Hasselfeldt, Hesse Prime Minister Volker Bouffier, and former Frankfurt Mayor Petra Roth. Some of these officials have also been named as possible successors to Chancellor Merkel in the event of a continued slide in her popularity.