Okay, so this is broadly true. Clinton's loss was so slight that changing any one of a number of things would have changed the result, and so you could blame any one of those things for being the 'critical factor'. But, more broadly... she should never have been in that position in the first place. None of them should have been critical factors! She was running against the most disliked presidential candidate in post-war American history, on the coat-tails of a largely popular incumbent with a good economic track-record given the context. It should have been a blowout.
The main factor wasn't Russia, or Trump, or rightwing propaganda, or Sanders, or Stein, or the electoral college, it was Clinton herself. She was an unappealing candidate who badly misjudged the zeitgeist and ran an incompetent campaign. Change any of those things and Russia can do all they like, the right can smear all they like, it wouldn't have been sufficient.
The more you blame all of those other factors, the more you're handicapping yourself for the next presidential election, since you're trying to absolve yourself of responsibility. You're the Principal Skinner of politics - are you out of touch? No, it's the electorate who are wrong. And the electorate will resent that. The way you need to treat it is to say, as someone who actually did become a Democratic President once said, the buck stops here.
Blaming Sanders for doing a better job at party unity than Clinton in '08 or Edwards in '04 does nothing. You couldn't reasonably have expected more of him, he delivered more than Democratic nominee opponents normally deliver. You also alienate the people who like him - which is the clear majority of the American electorate. He's the most popular national politician, and you're running away from him. It's dumb.