Most prevailing opinions in America run through our origins of "freedom" (a kind of libertarian free will) and some rooting for the underdog (which may have come from the fact that we are largely an immigrant-sourced culture)

As such, Socialism and Fascism are on the margins of popular opinion, implying government overreach and bullying. They occasionally succeed though, when there are eras of misinformation or hysteria.

As a moderate Dem, these are the themes I outline for my sons, so far successful:

Dems' pros

1) Reasonable climate and environmental controls

2) Some rational/limited allowance of abortion

3) Modest safety nets (medical, retirement, min wage)

4) Rational gun controls

5) Respect for other cultures, civil rights etc

Repub pros

1) Individual integrity

2) family values

3) Fiscal responsibility

4) Working hard, not complaining

Of course the Repubs four pros could easily be Dem's platforms too, and these value systems have traded party lines historically (ie civil rights, conservation, even pro-choice abortion were Republican themes in the 60s).

Currently, the 2 parties have skewed/contaminated these values (especially the Trump Republicans). Both parties have thrown fiscal conservatism out the window, both parties whine & blame excessively, etc.

I suggest that the value systems above are bedrock, and if they can't be supported by a 2 party system then a moderate party should be formed.