Trump apparently tuned into his personal network to see the Fox hosts pillory "crazy Bernie" in front of a mob of Trump supporters at a televised town hall event. He turned a deeper shade of orange on the greeting Bernie actually got from the crowd as the Fox shills were unable to control and humiliate Sanders as was their obvious plan. Apparently the average Fox viewer would actually like to pay less for healthcare that is simple and really provides for their needs instead of rich insurance executives.
Trump tweeted his displeasure but was out done by the so-called liberal establishment that was out in force to vilify Bernie for not being a team player and breaking the boycott of Fox. They were also willing to embrace Trump's conspiracy theory that the Fox audience warmed up to Bernie because they were really Bernie supporters and not actual Fox viewers.
Clinton apologizers won't admit that the 8% of Bernie supporters that didn't vote for Hillary were in fact Republicans, they instead prefer to characterize "Bernie-bros" as misogynists. In reality 15% of Hillary supporters refused to vote for Obama in 2008 calling themselves PUMAs (party unity my ass). If the math seems off on that it's because that Hillary has never been very popular despite the puffery and Obama was. Bernie becomes more popular as more people actually hear what he has to say and it drives conservatives nuts.
Establishment Democrats hate and fear Bernie and actual Progressives because they see their world going away if the middle-class ever comes to power again. A lot of them work in jobs that would no longer exist in a world where Wall St isn't allowed to scam people. An economy has evolved since Reagan where people at the top don't really do anything and get paid handsomely for it. A meritocracy just isn't their thing.