What were two of the key weaknesses of the Weimar Constitution?

The Electoral System - Weimar's Constitution used an electoral system of pure proportional representation. This meant that a party got a percentage of the seats in the Reichstag that corresponded with its percentage of the vote share. In theory, this sounds like the most democratic way to operate a Parliament - which is what was wanted in the aftermath of World War One. However, this lead to lots of small radical parties gaining 2-3 MPs in the Reichstag, with no single party gaining a majority. This meant that the German government could not get anything done, but also allowed radical parties a foothold in the Reichstag.Article 48 - this said that, in an emergency, the president did not need the agreement of the Reichstag, but could issue decrees. The problem with this was that it did not say what an emergency was, and in the end, it turned out to be a back door that Hitler used to take power legally.