I'll provide my perspective. First, the Democratic Party never "abandoned" the white working class or the poor. It's just that they broadened their party to be more inclusive of minorities rather than the "white working class" party that they were under FDR in the 1940s and continuing into the 1950s.
It started in 1964 when Lyndon Johnson signed the Civil Rights Act into law. That act saw much of the white working class (mostly Christian evangelicals) in the south leave the party because they could not tolerate sharing a party that embraced equality for African-Americans. That faction which was such a significant part of FDRs mandate was lost to the Republicans forever as the opportunistic Republicans welcomed them and their innate racism into the party.
The Vietnam War also divided the nation. Mention Jane Fonda's name and Republicans see red. She became another in a long line of liberals upon which Republicans could rally their faithful. Now it is more Hillary Clinton and Nancy Pelosi...a reason to hate liberals with manufactured bullshit.
Ronald Reagan carried on the tradition with his fictitious "welfare queen"...someone to hate. Not only the welfare queen but also government. Remember his quote, "Government is the problem".
As Democrats strived to become more inclusive of races, ethnicities, and women and gays as well as immigrants, it had an opposite effect with many in the white working class who saw them as a threat. If you have read Thomas Frank's book, What's the Matter with Kansas, you will understand how cultural wars were used to get poor working class voters to vote against their own economic interests.
On that latter point, it just didn't happen by chance. Lewis Powell wrote his infamous Powell Memorandum in 1971 outlining how conservatives -- the Chamber of Commerce and corporate activists can change the messaging by "building a powerful array of institutions designed to shift public attitudes and beliefs over the course of years and decades".
As per the link, "the memo influenced or inspired the creation of the Heritage Foundation, the Manhattan Institute, the Cato Institute, Citizens for a Sound Economy, Accuracy in Academe, and other powerful organizations. Their long-term focus began paying off handsomely in the 1980s, in coordination with the Reagan Administration’s “hands-off business” philosophy. Most notable about these institutions was their focus on education, shifting values, and movement-building — a focus we share, though often with sharply contrasting goals."
In other words, conservatives learned how to control the messaging by focusing on morality rather than getting bogged down defending their corporatist agenda. They learned to lie and cheat with an "anything goes" philosophy to gain power.
Donald Trump played that card beautifully telling coal miners, former factory workers and many others what they wanted to hear on "job promises" while deriding Hillary Clinton's policy messages. Hillary was 100 percent right on her proposals. Trump had no proposals...just promises that resonated including telling the Christian evangelicals what kind of person he is going to nominate to the Supreme Court. That promise brought out that faction to vote in droves...almost 90 percent.
Certainly Hillary also lost much of the messaging to Bernie as well, but Bernie also made promises that were impossible to keep. And if he had won the nomination, the ruthless Republican machine including the Kochtopus would have ripped into him and his baggage so hard he wouldn't have known what hit him.
The Democratic Party has been true to itself and it's roots. Those white working class Americans who abandoned the party for the "greener grass" and false promises by the "party of lies" have only themselves to blame. Even as the health care debate goes on and it appears many of those white working class Trump supporters will lose their helath care under Trumpcare, they remain loyal and steadfast.
The best Democrats can do is get out their base, but I am apprehensive about that as well because the Bernie Brats and their ideological "Our Revolution" does not seem to have lost any steam. In 2018 if the Democratic Party has not come together, expect Republicans to increase their majorities. And I for one will blame Bernie.