I've seen this claim numerous times and I guess we've all just bought in to the bizarre Orwellian definition of what "progressive" means these days, which is apparently a bunch of liberal issues OTHER THAN economic ones. This is the kind of crap that leads to conclusions like this.
But I read the Blue Rose Research report, and what do I see? Page after page of evidence that it is EXACTLY because the Democrats refuse to address class/economic issues - or what I at least would call "progressive" issues - that they lose. But it's worse than that.
Because the Democrats have fully embraced neoliberal ideology, politics, and policies for some 40+ years (Dem politicians prefer to speak approvingly of Reagan rather than FDR these days), their repudiation of the working class has resulted in profound voter alienation.
Only in a country where the so-called "liberal" party runs screaming from the legacies of the New Deal do we get surveys reporting that voters trust the Republicans more with Social Security, the economy, and the cost of living.
So, pardon me for being a contrarian the The Contrarian, but your interpretation here is just backwards. Or at least it is if we stop using the bogus definition of what "progressive" means.