I at least half agree. Sanders has been and independent (iirc) for about forever and has held his basic socialist views for as long as far as I know, but in honesty, I never actually studied him or paid a lot of attention to his activities. He has always been in a class of other independents who I had some respect for (Chaffee, Specter, to be specific.) I don't doubt that the establishment has animosity toward him, and it would probably nearly equal that which they feel for Trump if Sanders were an actual threat.
Depending on the craftiness of the Washington Insiders, Bernie wouldn't be a threat even if he were elected President. If worst comes to worst, the W.I.s can pull out one of Sir Humphrey's standard maneuvers:
1. When he first gets into office, let him do his thing. Stand back and let Bernie be Bernie. Neither advise nor consent, except with respect to implementation. Neither approve nor disapprove. But, work on a secret plan behind his back....
2. Now, Bernie has gotten his way. Since he's not a Washington Insider himself, it's a sure bet that the implementation of his New Bernie Revolution will contain at least one hugely unpopular screwup. Something like Mr. Trump's recent and walked-back "Todd Akin moment."
3. When the outcry gets to just the right volume, reveal the secret plan you worked on in stage 1. This secret plan is actually a plan that will save Bernie's political behind!
4. Put that save-Bernie plan to work. When the heat's off, and Bernie expresses gratitude, offer this kind advice: A President should always listen to the best experts and take their counsel seriously.
And back we go, to governing that looks and feels an awful lot like the political status quo ante. The Revolution Was.