I assume this would happen, when Hindenburg would decide not to run for a second term. Eckener would get the support of the Weimar coalition partys, SPD, Zentrum, DDP, maybe BVP and DVP. The question is, will it be enough, to defeat Hitler. The KPD will still run Thälman, so the Anti-Naziote is split. It can get close, I think the chances are 50/50.