In the election of 16 January 2005 Bahr was the SPD candidate for the office of Mayor of Neuruppin. In the first round he barely missed an absolute majority with a vote share of 49.80%. In the run-off election of 6 February 2005, he lost, surprisingly, against Jens-Peter Golde who united 50.26% of the vote.
MP
From 1990 to 1996, Bahr was on the city council for Neuruppin and 1993 the county Ostprignitz-Ruppin. From 1994 to 2009, he was member of the German Bundestag. From 1998 to 2002, he served as the speaker of the National Group of Brandenburg and the eastern German deputies in the SPD parliamentary group.
In 1994 and 1998, Bahr was the representative of Neuruppin-Kyritz-Wittstock-Pritzwalk-Perleberg. Since 2002 he has represented Prignitz-Ostprignitz-Ruppin-Havelland I in the Bundestag. In the Bundestag election of 2005 he recorded 38.5% of the primary vote.
In the federal elections of 2009, he did not run for the German Bundestag. He was succeeded by the current vice-chairman of the SPD, Dagmar Ziegler.
Public offices
Bahr was District Administrator of District Neuruppin 1990–1993.