The Democrats' coalition of the ascendant did not ascend. Hispanic voters did not overwhelm. Black voters did not deliver. Rural and working-class whites abandoned the party in droves.
The Democratic Party is dependent on the presidency. Without it, the multi-racial, multi-class, water-hugging, tree-hugging party of the 21st century will enter 2017 obliterated, clinging to California as a government in exile as Washington falls to a political opponent that no longer looks like the Republican Party of even 2014, and may prove to be something American democracy has never seen.
Without the executive branch, or one side of Congress, Democrats are stranded, with no probable path to power before the next presidential race. (Their 2018 Senate prospects are grim.) Who knows what Trumpism will produce by then?
American institutions, Wall Street and corporations are in a nervous fit now; the markets are revolting. But they can be soothed, part way at least, with the right words, and as president Donald Trump would know enough to murmur them. Business will defend itself, but won't defend Democrats.