Short answers, pulled from the story.
The Enabling Act of 1933 was a German law that gave the cabinet, headed by Adolf Hitler, the power to enact and enforce laws without the involvement of the Reichstag or President Paul von Hindenburg. It effectively bypassed the checks and balances of the Weimar Constitution and transformed Hitler's government into a legal dictatorship.
The Nazis secured the required two-thirds majority through a combination of coercion, bribery, and manipulation. Communist deputies were excluded from the quorum count by Reichstag president Hermann Göring, many SPD deputies were arrested or in hiding, and the Catholic Centre Party was persuaded to vote in favour after Hitler's negotiations with its chairman Ludwig Kaas on the 22nd of March 1933.
Only the Social Democratic Party (SPD) voted against the Enabling Act. The final tally was 444 in favour and 94 opposed, with all 94 no votes coming from SPD deputies. Twenty-six additional SPD members could not vote because they had been arrested or had fled into exile.
Otto Wels, leader of the SPD, was the only party leader to speak against the bill in the Kroll Opera House on the 23rd of March 1933. He defended the Social Democrats' record after the First World War and declared: "No Enabling Act gives you the power to destroy ideas that are eternal and indestructible."
The act's legal validity has been disputed. British historian Richard J. Evans argued in his 2003 book The Coming of the Third Reich that the act was legally invalid because Göring illegally reduced the quorum by refusing to count the 81 absent KPD deputies, and because the Reichsrat's assent was tainted by the prior overthrow of state governments.
Germany's Basic Law of 1949 was written specifically to prevent a recurrence. It stipulates that only constitutionally empowered bodies may enact laws, and it requires that political parties be declared enemies of the constitution only by the Federal Constitutional Court, not by a parliamentary majority, preventing any popular majority from legally installing a totalitarian regime as occurred in 1933.