The reason Democrats are getting so nervous is they inherently know Clinton is so unlikable, her support buttressed by loathing of Trump as the greater evil is only an inch deep. If it cracks, it sinks hard into the 40's.
I don't think that's what's happening here, but the fright is somewhat understandable (albeit still mostly over the top).
I don't think thats what Democrats are wetting the bed about. It's not that we believe that our candidate is inherently unlikable, we're just distraught by the fact that Donald Trump is the second most likely person to become POTUS come November 8th.
To put it bluntly.
A lot of us believe that the stability of our Republic hangs in the balance. Most of us don't think Hillary is going to lose, in fact, most of us believe she's going to win by a comfortable margin. Any chance of Trump winning this election, no matter how small, is enough to make us nervous.
Exactly the way I feel. It needs to be large enough to turn back the tide of extremism and anti-governmentalism or the next 4 years is going to be really ugly.
Then stop panicking and do what you can to change things. Trump is where he is thanks to the GOP, if people hold their nerve and work as hard as they can, Trump isn't going to win. It really is that simple.