The Washington establishment threatens businesses. They extort billions of dollars from businesses by threatening business. Sanders is a communist but so are many members of the Washington establishment. Communists paid for Bill Clinton's trip to Moscow in 1970 to meet with Soviet Party officials. The Clintons received billions from Communist China and gave China U.S. military technology. John Kerry worked with the Communists throughout his career. Democrats sabotaged Reagan's cold war efforts and helped the Communists. Most Democrat establishment types are Communist sympathizers.
Senator Sanders is the ranking Democrat on the Veterans Affairs subcommittee. He has used his position to defend corruption by insiders in the V.A. and prevent veterans from getting medical care.
Senator Sanders is a corrupt Washington insider. He is a member of the Washington establishment. He is for the status quo and Obama administration programs.
The MSM do support him and his position as Senator. The MSM dishonestly portrays him as an outsider. It is a lie.
When you look at all the newspaper endorsements Hillary is getting, it's hard to say that Sanders is the Establishment's choice for president.
While not everybody in Congress is a full-fledged member of the Establishment, a senator or representative who wants to be anti-Establishment really has to work at it.
If you vote the way the party wants you to, don't make waves, and manage to get elected enough times, you aren't going to be seen as anti-Establishment.
If you run for president and antagonize the party's leaders and money sources, you may qualify as being "anti-Establishment."
I see your point, but compared to Obama or John Edwards, let alone Hillary, calling Bernie an insurgent or a maverick wouldn't be wholly ridiculous.