I'll explain. It works on two levels.
It promises something Bernie isn't doing so it scares people who aren't sure about him to vote for Trump.
But here is where it gets even better. Even if it fails to do it's surface level propaganda, it can be reused as an excuse that Bernie didn't meet his promise to make everything free and everyone else pay for it!
You know who else promised free stuff and that someone else would pay for it? Trump with his wall with Mexico. Now, I can't remember, but didn't every Democratic candidate admit that raising taxes would probably affect the middle-class too? That doesn't sound like everyone else is paying for it. Sounds like everyone is going to paying for it.