Constitutional Problems of the Weimar Republic
The Weimar Republic had many problems. First, the chancellor was given power to act without consent of the parliament in emergencies, as a way to diminish party politics. Also, a law did not have to conform to the constitution of the Weimar Republic if two thirds of the parliament voted for it. Proportional Representation allowed many small parties to gain access to parliament. The parliament also could elect to impeach the chancellor without voting a new one in.
The chancellor had the emergency clause, where he could "take all necessary steps" if "public order and security are seriously disturbed or endangered." As you can see, this is a very vague clause and if interpreted in a loose construction view it allows for pretty much anything. Hitler used this clause many times in his rise to power as a dictator.
Another problem with the Weimar Republic’s Constitution was that a law did not have to conform to the constitution if it had a two thirds majority vote in parliament. If one party, such as the Nazi party, were to control a two thirds majority, then they could easily pass unconstitutional laws.
Proportional Representation is the practice of giving a party or state a proportional amount of representatives compared to the population that is in the given state or party. This led to many small parties, which bogged down the lawmaking process because they could never agree on anything.
Finally, the chancellor could be removed by the parliament even if it was unable to agree on a successor. This led to a state with no head, which impeded decision-making immensely.