Was Hitler elected by the democratic process? I suppose, but really only in the Tammany Hall (JFK?) sense of the word.
- The German Communists were one of his chief competitors: he successfully framed them for the Reichstag fire and made them (basically) illegal.
- The same act which allowed him to boot the communists gave him authority to detain members of the Social Democrats (other opponents)
- Hitler lied to the leader of a third major party, leading to his endorsement of the plan which allowed Hitler to take the helm.
- The Night of the Long Knives, after the elections, removed many people opposed to the Nazi party.
So, with one opposing group illegal, another crippled, and a third deceived, he was able to gain legislative and executive control of the WeinmarWeimar republic with a clear 5 to 1 majority in parliament.
Once he had this, it was trivial to either coerce opponents to "voluntarily" step down or, in some cases, forcibly remove them to concentration camps.