Hindenberg needed a small party to partner with in order to form a gov’t, and selected the Nazis, reassuring his colleagues, “don’t worry, I can handle Hitler.” Oops.
IIRC, the liberal dream of broad democracy and a fecundity of small parties had finally arrived in Germany. It was that splintering of German politics into minute identity groups that allowed the Nazis to win a minority-majority election.
Not learning from history...
Meanwhile, Von Papen was using Hitler to get back at his rival Von Schleicher. And Hitler took advantage of the bickering to engineer a behind-the-scenes coup.