You cannot get votes from people you hate
I come from a white working class background. While I did not vote for Donald Trump, the white working class is the group of Americans that most strongly supported Trump last year. Much has been written about whether Democrats can win that demographic, but it goes much deeper than policy. Democrats will never win that group until they stop hating the people in it. You can moderate your policies, and adopt policies to economically benefit the white working class, but voters simply will not support politicians who hate them.
Part of the anger against the white working class (WWC from here on) is that Democrats are bitter because they think the WWC owes them their votes. Democrats have always been the champions of the WWC, the thinking goes, so they feel betrayed. But the phenomenon of the WWC abandoning Democrats did not start with Trump. A significant shift took place in 1994 with gun owners upset about the Brady Law and the "assault weapons ban," which riled Democrats even more and fueled bigotry. Does anyone remember Barack Obama's remark in 2008 about WWC voters clinging to guns and religion?
But it goes deeper than one issue: It is an antipathy for rural white voters, because many Leftist elitists do not think WWC voters have the proper pedigree to even be active in politics. There is a reason a local state representative (and a friend of mine since my college days) has been called "Jethro" for as long as I can remember. Elitists in Bloomington (especially in academia) hate him not for his stances on the issues, but because he is a little too "country."
I have experienced this personally. Some of my harshest critics were angry with my political involvement because they saw me as a hick from a little hick town, not worthy to be debating with the college-educated "elite" in Bloomington. The fact that I have a college degree does not matter. What matters is I was not from the right background. It was not my politics they were angry at, but that I was not staying in my proper station. Is it any wonder that Donald Trump won the WWC voters that Leftists have sneered at for so long?
The problem Democrats have in reaching white working class voters is not that WWC voters have a problem with Democrats' stances on abortion, gun control or identity politics. The problem Democrats have is that they see white working class voters as beneath them and unworthy of being included in our national political conversation. That bigotry is not something they can hide. Unless Democrats purge the bigotry of elitists in their party, all of their efforts to woo white working class voters are doomed to failure.