US Stem Cell Inc (USRM)

[JPL1868]

Yes, it’s possible. Depends on the broker and margin requirements.
It’s typically MMs that are shorting though. All shorting is is borrowing shares you don’t have to sell to someone else. When doing this, you’d obviously want to buy those shares back for less than you sold them for. But MMs need to fill orders so they often borrow shares to sell them will try to manipulate the price lower in an effort to cover.