I think that there is a lot of faulty analysis here. Trump is not and never has been an economic populist. That isn't his appeal to his base. His tax cut was huge and helped the base almost not at all. The Trump administration went against the spirit, and probably the letter, of the CARES ACT in tilting the aid to large business and providing earnings to big banks who sponsored their customers. None of this was consistent with economic populism. Nor is this at all similar to Bernie's proposals, which actually aim benefits toward the poor and middle class and disadvantage large corporations and the top 5%.
The largest portion of Trump's base are straight, white, traditional, literal, conservative Christians -- largely the white evangelicals, but also the conservative Catholics, who have never accepted the loss of the Latin Mass or the election of the current Pope. Their theology does not oppose accumulation of wealth by the top 1-5%, as Bernie does. They see it as a sign of hard work and God's favor. These are people who view economic populism as evil socialism. They are populists, but they are cultural populists. They favor the plutocrats, but don't like minorities, liberals, intellectuals, and women who have advanced from their prior station. These are the cultural warriors. They oppose abortion, generally oppose birth control and sex ed, were virulently opposed to gay marriage and equal rights for LGBTQ. They are basically not reachable. When they talk about liberal elites, they mean those who set a culture in America which differs from their own. They dislike educated professionals, who place other sources of knowledge and decision making above the bible and the way their pastors interpret it. They fell behind Trump in higher numbers than behind the actual pious white evangelical GW Bush, because he promised to let their leading pastors set the agenda on social issues. There were no economic demands made upon Trump. A lot of these people panicked when they saw that in 2 to 3 decades the share of whites in the population would fall below 50% and that the share of regular church goers was expected to continue its decline.
The second largest group in Trump's base are small business people. They are conservative economically. They want taxes, expenditures, and regulations that promote their success. This is a group which Trump has helped economically. I suppose the Dems could tailor an economic message toward them, without losing their own base, although this is difficult because the small business people are adamantly against raising the minimum wage and, in general, focusing upon environmental issues -- global warming, but lots of others.
The third segment of the Trump base are the macho men and the women who love them. They are attracted to Trump's big personality and bullying.
Trump also got a lot of what I'll call regular Republicans. People whose families have been Rs forever, CEOs and other top managers and earners. The folks who actually are the economic elite. The no limits on guns people also fit in here, although gun owners who support reasonable regulation do not. The Ayn Rand crew, and the Rand Paul crew, also fit in here.
When they aren't fund-raising among the economic elite, which the post-Citizens-United world almost dictates, Dems have remained largely populists on the economic side. That just doesn't sell with many of those who used to be white working class, since their politics is now guided by their cultural populism -- they want preference for white, straight, Christian males to go back to the levels common in the 1950s. They want to set the cultural atmosphere.
Some of thee people did vote for Bernie in the Dem primaries -- not because they favored his economic populism or socialism, but rather because, like Trump, they saw him as somebody willing to burn down the system, giving them a chance to rebuild it more to their liking -- but focused on the cultural, including education, system.