This gives the GOP far too much credit. They've spent the last four years dead certain Hillary would be the nominee (and I don't blame them; everyone has felt this way) and have rightly put their efforts towards torpedoing her campaign. Sanders doesn't have any dirt because nobody thought to dig up dirt on him. They are actually terrified of a Sanders nomination, because his message is extremely populist and they have no way to fight back on policy. Sanders would have them caught with their pants down.
In fact the *only* ammunition they have against Sanders is calling him an extremist socialist over and over (while he calmly explains that his ideas aren't very different from what we've done in the past...). The only voters that's going to convince is their right-wing constituency who would never vote for a Democrat anyway, even if Ronald Reagan himself rose from the grave. It's the undecided they have to convince, and his voting record has him on the right side of nearly every unpopular decision over the last 20 years.
Ummm... attack ads, the media establishment and TV debates that are shaped by personality and strong held convictions determine presidents. The socialist label reeks and it's being underestimated greatly. 15 minimum wage? socialist. Universal healthcare - socialist. "Shouldn't surprise anyone "Bernie is a self-proclaimed socialist"". His whole record will be characterized as that of a commie-socialist. "The communist win if you elect Bernie" - lmao...I can see that being an ad.
The attacks will not stop, they will be vicious and he will have to confront them on a debate stage, not a rally stage of liberal followers who don't put as much weight on that word, nor challenge it. Any moderate republican will be seen as a godsend even with the baggage...namely, Jeb.
You know what they'll do to Hillary: Benghazi 24/7, not fit to be president. Private server 24/7 - untrustworthy. The general populace is already aware of it more or less. Will it come as a shock on election day? More like tired vitriol.
Every politician has dirt. Just a matter of digging, twisting and lying the right way (aka negative attack ads). I don't know, I just don't think the country is ready given the current environment. I do think as the country leans more blue in the next 10 years or so candidates proclaimed socialist with socialist leaning policies will become more and more electable. Today, for president, not so sure. And Bernie is NOT Obama 2.0 - not as good of a speaker, not as young or energetic etc etc etc. He's an old white senator from Vermont with progressive/socialist leaning policies that appeal to the far left and also happens to NOT be Hillary (for the Dems that want their message carried by anyone not named Hillary).