Ever since it was known that Donald Trump had won the presidential election (thanks to the archaic electoral college), some media and political pundits have been trying to write an obituary for the Democratic Party. They want you to believe the Democratic Party is in disarray, and could be a dying institution. Nothing could be farther from the truth.
First, a couple of reminders. Donald Trump actually lost the popular vote to Hillary Clinton (the Democratic candidate) -- and it was by a pretty substantial margin (nearly 3 million votes). Trump won because he got a razor-thin majority in a few states -- enough for an electoral college victory.
The future is actually pretty bright for Democrats. Look at the exit polls above (from cnn.com). Trump's biggest support came from Whites and older Americans. He led among White by 20 points and by those 45 & older by 8 points. Guess what -- both of those groups are shrinking. Whites become a smaller portion of the electorate with each election, and those over age 45 will die off.
Meanwhile, Clinton (i.e., the Democrats) did better among Non-whites and younger voters. She led among Non-whites by a staggering 53 points, and among those under age 45 by 14 points -- and both of those groups are growing in size. With each passing election, Non-whites make up a larger percentage of the electorate, and as older voters die off they are being replaced by younger voters (who can't abide the Republican Party's social or economic agendas).
The Democrats didn't do a very good job of effectively communicating how their policies are better for workers (and all Americans) -- and they need to do a better job of that in the future. But the demographics are with them. If they can combine those good demographics with a better communication to voters (and I believe they can), then the future is actually quite bright for the Democratic Party.