Democrats looked at the demographics and made an explicit decision to toss out blue collar (and now even white collar a la H1b) workers in favor of immigrants and corporations. The only difference between the Republicans these days is the Republicans don't hide behind their agenda by labeling those who disagree as bigots and uneducated idiots.
You can only call someone a racist, xenophobe, while they are training their own foreign replacement, for so long, before it loses effectiveness.
Do the Russians have organizations tasked with influencing foreign policy in their favor? God damned right they do, just like every major nation state on Earth. The US, btw, dwarfs the rest in this type of work.
Do these types of influence work in a vacuum? Not as well as they do when a demographic is already teetering on the edge.
Bill Clinton and the neoliberal DLC did, and it's been the source of a lasting divide within the Democratic Party (the party-in-government, not just the party-in-the-electorate) since; see, everything from the vote oj NAFTA through the 2016 Presidential primary and the subsequent DLC leadership campaign.
While the neoliberals are still the dominant faction within the Democratic party, they've lost ground to more strongly pro-labor progressives recently (compare 2008, when both leading primary contenders were soldily in the neoliberal faction to 2016) and there's plenty of reasons to think that will continue.
If you're going to tell me that brainwashing is not a thing, then explain how advertising exists as a billion dollar industry.