This last sentence is something I see repeated a lot, and I think it's way over the top. From around February 2016 through a month ago people would have said the exact same thing about the GOP except in far more severe terms.
How many magazine cover stories were dedicated to the demise of the party?
The Dems are somewhat rudderless right now, but they have
plenty of time to work it out. And they're coming off an election in which they won the popular vote for president by almost 3 million votes and gained seats in both the Senate and the House. They got victimized by a combination of strategic errors and terrible luck in the presidential election, as is usually the case in upset victories, but if our country and our basic framework for government remains in place over the next few years (a bigger if then we want to acknowledge, IMO) they'll be just fine.
They'll probably lose some Senate seats in 2018 just because of the quirk of the cycle/map, but I bet they make decent gains everywhere else, including important state races. Opposition parties who don't control the White House or Congress always do very well at midterm elections, even with presidents who aren't nearly as widely despised as Trump (see 1994, 2006, 2010). And
the Senate gains will come two years later, probably.