I agree that the leftward shift of Democrats will hurt the party with the voters who considered Trump, but more because Democrats depend upon news media and big donors, which you simply ignore. Fox News alone is not responsible for those voters who think Tea Party rhetoric or Trump might shake things up, those mostly white voters doing a little better in places that are doing poorly, falling behind, and who are aghast at the economic and social changes they see around them.
The news media that still fear mongers about debt and the virtues of cutting entitlements will squash any efforts to teach voters that welfare chauvinism and boom/bust is more expensive than more progressive policies and more public programs (universal with oversight).
Do you expect news media to greatly reduce the obsfucating of the differences you hope voters will eventually see, between states that expanded Medicaid and those that did not? Those helped by Medicaid and doubling sliding scale clinic funding would need a Congress full of Bernie Sanders to explain it to everyone else despite news media, meaning politicians whom big donors and news media campaign against harder than Russians.
News media (again, not just conservative right wing news media) already makes sure that voters do not see how stronger financial regulation (and tax reform to make the economy distribute income more fairly and grown more productively and sustainably) will affect their pocketbooks and future. Trump is only making (and poorly) arguments that TV news gives oxygen to, endlessly resurrected, dressed up “government is the problem” arguments.
The Southern strategy can other people of color, women and the less educated, if not quite as easily as blacks in the South. News media is careful not to challenge the othering of BLM or climate activists no matter how right (see how many WaPo readers pay their subscriptions and continue calling them terrorists), teachers unions, and anyone so naive or hippie to appreciate why raising the SS cap makes SS stronger than Hillary Clinton’s hints she’ll mean test to help a subset. Without news media, would 97% of Trump voters, who use an average of 4 public programs that subsidize them, be certain they have never relied on entitlements or government help?
News media will continue to make sure that voters think public-private infrastructure investment may be more efficient and effective. News media will continue to make sure that voters think privatization and devolving power, regulation and tax revenue to laboratories of democracy (throwing “Swimming for Dummies” books instead of life preservers to drowning regions) are worth trying. Why ignore the news media that has not even shot down for the general public the notion that there must be some way to sell health insurance across state lines so people can keep their doctors? It’s not just that right wing news media or Murdoch’s WSJ is telling us that 2 + 2 could equal 5, because television news makes sure those who can’t do arithmetic get credence.
By the time news media informs voters that raising the minimum wage is a win-win, how much more redistribution will have been promoted and allowed to happen? Sorry to sound so negative, but until you can get around news media, I’m not sure how much Democrats’ incrementalism will advance the progressive policies, the ones that will keep a smarter “conservative” from making better inroads with voters than Trump has made.