i don’t think the democratic party is being weakened by this election. the biggest threat to the democratic party is going to be from an influx of former republicans looking for somewhere to go if the republican party breaks up into a trump/tea party faction and a traditional republican faction. especially of the trump faction gains the upper hand in the party hierarchy. you have to know that the greatest hope of the establishment republicans is that trump just doesn’t have the attention span to turn the party in his image.
the state legislatures are probably the greatest threat progressives face from this situation since many of the most important voting blocs in the democratic party don’t get out and vote during off-year elections which is when most state legislatures have their elections.