Critics and politicians of other parties have repeatedly criticised him over the links between his political and business activities,[1] for example when he advised the IKEA group about its plans to establish itself in the East of Berlin.

The scandal concerning Wolfgang Antes (CDU) who was in charge of construction in Charlottenburg figured heavily in the media.

His support came from a Red-Green coalition between the SPD and the Alternative List (AL) (the former Berlin equivalent of the Greens).

The foundations for the growing together of the two halves of the city and Berlin with the surrounding area was agreed on 12 December 1989 when Momper met Hans Modrow, the Prime Minister of the GDR, and the provisional Regional Committee was established as the first cross-border body.

After the police had cleared a series of squats on the Mainzer Straße on 14 November 1990, the AL announced that it would not go into coalition with the SPD, since both Momper and the Innensenator concerned, Erich Paetzold (SPD) regarded this action as sound politics.

The SPD ended up ten points behind the CDU, whose leading candidate Diepgen, Momper’s predecessor, was then elected mayor again on 24 January 1991.

Momper remained SPD state chairman, but finally resigned on 17 August 1992, when he went into the real estate business.

In 1995 he put himself forward in the internal party primary election of the Berlin SPD to be the party's lead candidate for the Berlin House of Representatives elections, but was narrowly defeated by Ingrid Stahmer, the Senator (city councillor) for Health and Social Welfare.