Backed by Chancellor Angela Merkel’s conservative Christian Democrats, Koehler, 66, is seeking a second five-year term for the largely ceremonial post.
Under Germany’s constitution, the head of state is chosen by a
1,224-member electoral college called the Federal Assembly.
The panel comprises all the 612 members of the Bundestag lower chamber and 612 public figures, a few of them sports heroes and television actors, nominated by Germany’s 16 federal states.
During the balloting, Merkel’s coalition with the centre-left Social Democrats, which has ruled Germany with remarkably little discord since 2005, will temporarily cease to apply.
The Social Democrats have decided against voting for Koehler, and have instead nominated academic Gesine Schwan, 65, creating a re-run of a competition that took place five years ago.
She has been stumping the country for months, wooing support from potentially wavering electoral-college members.
Two opposition parties, the centre-right Free Democratic Party (FDP) and the Bavaria-only Free Voters (FW), have swung behind Koehler, ensuring on paper that he will have a two-vote majority.
But it is not certain all the FW voters will fall into line in the secret ballot.
Koehler’s chances of victory improved on Friday when the leader of the hardline Left party, Lothar Bisky, did not rule out some of its members voting for the incumbent, even though the party is fielding a candidate of its own, actor Peter Sodann.
If none of the contenders obtains an absolute majority in the first ballot, there will be a second round of voting in which a simple majority will suffice.
Koehler, an economist who once headed the International Monetary Fund (IMF), is generally perceived as a popular figure although he has occasionally upset conservatives by criticizing big business.
He has also used his powers to hold up legislation when constitutional court challenges to it were still pending.
If he were to lose it would be a major upset for Merkel as she prepares to campaign for a general election on September 27. (dpa)