This is delusional thinking. Like her or not there isn't a single legitimate threat, Sanders included. Really the only name that was being thrown around that stood a chance was Warren. Barring complete self destruction on her part Clinton will win with ease. Unlike the last election there is no one with the same charisma as Obama (or Edwards for that matter). For the record ideologically I'm probably closer to Sanders than Clinton but I'm also a realist.
I see Sanders as a legitimate threat. Remember when we all thought that she had it in the bag at this point in 2007 against Obama?
There is a degree of self-destruction already with Hillary's campaign because it looks like she hasn't learned a damn thing from her failed 2008 campaign. Her campaign is acting like she has it nomination guaranteed....again! The way she is brushing off legitimate concerns like her recent e-mail scandal is mind boggling. Sure, she's pivoting to the left because she has no choice due to the party's base becoming more leftist, but she comes off as totally fake and phony in the process. I highly doubt in the time between her retirement as Secretary of State to today that she went from being the epitome of Wall Street Democrat to progressive champion. It's absurd that the one person she is essentially running against, is her husband Bill Clinton, while acting like she's the return of the Clintons. While you can agree or disagree with Sanders, at least he's standing for something and comes off as a human being.
There is also a potential image problem with Hillary's campaign that they aren't dealing with such as how she is being comedically portrayed. Just look at Kate McKinnon's version of her on SNL where she comes off as some weird, power-obsessed robot. It's just like how the media portrayed Romney as completely out of touch or Sarah Palin as a complete moron. It doesn't matter if such portrayals are true or not, but they leave a lasting impact and Hillary's campaign is doing nothing to counter it.
The other problem with Hillary's campaign is that there is just nothing to get excited over with her candidacy. People who are excited over her are just excited over her because she's either A). A woman or B). A Clinton (even though she is denouncing everything that her husband did as President). At least people who support Sanders are getting excited over what he's offering.
And dare I say, expect Sanders to do well among college towns and if he plays his cards rights, blacks because they're more likely to lean ideologically towards him than Hillary.
EDIT: That said, Sanders will be a complete disaster in the general election.