Scott Lemieux has a good post overviewing and refuting claims that Democrats are responsible for Republicans nominating neo-fascist extremists like Doug Mastriano in Pennsylvania. The argument in favor is that some Democrats have spent money on ads which supposedly "boosted" Mastriano over his primary foes. This, critics continue, is recklessly irresponsible insofar as Mastriano is, again, a far-right lunatic whose presence within a country mile of levers of power would be an existential threat to democracy.
The problem with this argument is that the ads in question are attack ads against Mastriano. They are clear and forthright that Mastriano is a neo-fascist extremist who represents an existential threat to democracy. They nonetheless "boost" him because Republicans like all of these things. But that's a problem with Republicans, not Democrats. As one commentator pointed out, it's one thing to run an ad that lies about the health benefits of poison -- if people ingest the poison, that's on you. It's another thing to run an ad that says "poison is dangerous!" only to witness scores of people say "actually, I love poison, I'm going to take a double dose!" That's on them.
The fact of the matter is that anti-democratic fascist flirtations are an overwhelmingly popular position amongst the GOP primary electorate. Mastriano's closest contender in the GOP primary was Lou Barletta, who is himself a far-right figure with a history of White supremacy. There was no constituency amongst Republicans for a non-poisonous figure, so Democrats hardly committed some foul by trying to inform the general electorate of who Doug Mastriano is.
Lemieux's post covers pretty much all I want to say. All I'll add is that we're just seeing the extension of the infantilization of the American right; perhaps the defining feature of American conservatism over the past six years. Republicans make terrible choices and then whine that Democrats aren't better babysitters. But that's not the job of Democrats. Republicans are adults, they can make their own choices, and they are consciously choosing to promote candidates with Nazi ties and fascist sympathies. That's bad. That's also their own decision, and trying to fob responsibility off onto Democrats is pathetic.