Well once the Depression set in, you've got more people in the general population voting for the extremist parties, who seemed to offer a better alternative to the SDPs and parties that supported democracy. And you have to remember that von Schleicher was a leading army rep who exerted a great influence over Hindenburg and his decision-making. And remember the flaws of proportional representation.
Heinrich Bruning - after Muller resigned, Bruning was selected to head a new Cabinet (on von Schleicher's advice). Most important things were his deflationary policy and the frequent use of Article 48 to rule by decree now.
However, it seemed as though Bruning had failed to solve these economic problems and their ever-reliance on the SDP for support meant that Schleicher thought it was the end of Bruning's reign.
Then came von Papen, a friend of Hindenburg and his cabinet was filled with conservatives [note the rise of the Nazis as well]. After the snap elections of 1932, Papen was left with a small number of seats and Hitler demanded the chancellor role. You've got more instability so Schleicher was convinced somehow that Papen had to go, and that the Nazis had to be in power as well.
Schleicher is elected, attempting to split the Nazis with a deal with Strasser. Papen felted betrayed by Schleicher's act so he worked with Hitler to finalise a deal, and in the end, it resulted in Schelicher being supplanted by Hitler in January 1933.
