The election for the largely ceremonial post, which falls on the 60th anniversary of the creation of Germany's democratic constitution, is decided by a secret ballot of 1,224 parliamentarians and other public figures belonging to the so-called Federal Assembly.
Köhler, a member of Chancellor Angela Merkel's conservative Christian Democrats, is considered a dependable and likeable president who has her backing for a second term despite ruffling feathers with occasional broadsides against the political class.
The 66-year-old former head of the International Monetary Fund will likely get another five years in office, but there is ample room for an upset that would reflect badly on Merkel.
There are two other candidates, the most dangerous of whom is the centre-left Social Democrat Party's (SPD) Gesine Schwan.
“Köhler has a small advantage but it is not yet sewn up,” political scientist Jürgen Falter at the Johannes Gutenberg University in Mainz told news agency AFP. “It would be an enormous signal if Gesine Schwan were to win. It would boost the SPD and the end-goal here is the general election.”
But critics – some within her own party – say Schwan's chances are shrinking after comments she made to daily Bild claiming that former East Germany (GDR) was not an unjust state.
“There is no doubt: the GDR was a dictatorship and an unjust state,” SPD parliamentarian Ernst Bahr told Bild on Wednesday. “I will make my opinion clear to Frau Schwan.”
Hubert Aiwanger, head of the Free Voters, an association of unaffiliated voters, distanced his group from Schwan due to her comments.
“The GDR sentiments disqualify Schwan for the post,” he told the paper. “The position of our ten voters for Köhler is now clear.”
Peter Sodann, a former TV cop on the popular TV series Tatort is the hard-line socialist Left party's candidate, but he stands to get less than five percent of the vote on Saturday.