The GOP will go hard and constant against Sanders' atheism and Socialism, so its relevant and greatly reduces his chances to get the swing votes required.
there are no "swing votes", that is a collective delusion held by the political establishment, so it's also irrelevant.
Sanders has faced nothing remotely close to the propaganda campaign that will be launched against him if he gets the nomination, and they have facts against him that matter to those swing voters.
"swing voters" if they even exist (which i doubt) are a tiny, tiny minority of the electorate and are utter irrelevant to the outcome of an election.
and what "facts" do they have exactly?
'omg, hey, listen! people who agree with raising taxes and implementing collectively beneficial social programs! bernie sanders is gonna raise taxes and implement collectively beneficial social programs! BOOGITY FUCKING BOOGA!"
Sanders will get damaged in the general and his only chance will be if the GOP nominee can be damaged more by the Dem strategy.
damaged by what exactly?
The GOP is evil but smart and win far more offices than they reasonably should because their propaganda strategy is consistently more effective.
i disagree on the logistics of this - they win far more offices than they reasonably should because most citizens of the US are functionally retarded.
There is only one plausible reason why the GOP is going harder after Hillary than Sanders now and in the past few months. It is because their best research tells them that they can beat Sanders much more easily in the general, so they want him to win.
no, it's because their best research tells them that attacking that uppity bitch who thinks she deserves to be president will get their based more fired up (and thus more likely to vote) than attacking the guy from Curb from your Enthusiasm.
the facts about the candidates don't matter when it comes to the election, so it's really all totally irrelevant.
take the voting public (i mean the people who actually go and vote) - across the country it's 45% democrats, 45% republicans, and 10% morons who vote for the Green or Libertarian party or whatever the hell those jackasses do.
elections are decided by which percentage of the 45% bothers to show up to vote... thus, elections in the US are based around nothing more than which part feels generally more aggrieved and motivated to bother going outside.
swing votes do not exist, independents do not exist, elections are not won or lost based on the policies or histories of the candidates - winning an election just comes down to being attractive to your party's base, and not fucking up so badly that you become unattractive to your party's base or energize the opposite's base against you.