I'd love to see how they try to argue it now.

While I am a leftist (not a liberal nor a tankie retard) imma talk from history (I'm autistic about this)

in a spark notes version basically the party switch can be in thanks due to the northern Democrats who were more pro civil rights unlike the southern Democrats who were not, southern Democrats who felt like the northern Democrats who were becoming the majority were too much like the Republicans

though we can also attribute this to FDR who's new deal offered progressivism that was scene as something new to the Republicans who were more of an ideology called "liberal conservatism" which is socially conservative but economically more classically liberal

The Myth of Democrats as “The Working Class Party”

It’s trendy to imagine Democrats as champions of the little guy. Yet historically, the party has had deep ties to the powerful:

The “Solid South” leaned on railroad magnates and cotton kings.
Tammany Hall ran on patronage and big corporate donations.
In recent years, Big Tech, Wall Street, and Big Pharma have overwhelmingly favored Democrats in political contributions.

FDR’s New Deal didn’t dismantle monopolies; it often protected them, erecting regulatory walls that smaller businesses couldn’t scale. Influence was — and still is — often redistributed upward. The only thing Democrats have ever consistently redistributed is influence — from voters to big donors.