Why can't Dems presidential hopefuls pull this much people for any of their rallys? <20,000+

[GProgrammer]

Is that 20,000 people according to trump, or the fake media?

20,000 eh?
Here a recent Bernie Sanders crowd,
https://www.youtube.com/watch?v=5Oix_dTW3dI20,000 - 50,000
In trumps words

SAD