alt Hacker NewsShorts don't cost much to open, just the borrow rate on the shares. As long as it goes straight down you can leverage quite a bit without getting called.
Of course, this is the fastest way to lose your shirt and everything you have ever worked for, if there is any uncertainty.
Yes, I'm sure Robinhood or Schwab will allow me to open a $2M short position when my portfolio is $[sufficiently small that I'm debating the costs of a couple of thousand for a helicopter charter].