Democratic fatigue, in the sense that the progressive base of the Party is not excited by Obama anymore, and has never been excited by Clinton, has already set in. That said, demographic changes among upcoming voters suggests that Democrats, no matter how unpopular they become as a Party, will continue to win Presidential elections. George W. Bush may be remembered as the last Republican President, especially if the Libertarian party emerges this November as a viable third party, and receives 5-10% of the popular vote. The GOP, at that point, will either have to adopt some of the Libertarian platform, and hope their social conservative base follows along with them, or they will become irrelevant on a national level.
Of the election years in the poll, I would say it is entirely possible Democrats will hold office until 2028, if Trump loses this year.
Really? Maybe not the fridge Sanders nutjobs. But, his approval rating suggests that most progressives are quite fond of Obama. Sorry he's not cutting American jobs so that he can save a tree.,