Yes, as well as routinely banning conservatives and libertarians. They even shadow banned Scott Adams, a liberal, who endorsed Trump because Clinton's corruption and lying made her unacceptable to endorse.
WikiLeaks Makes DNC Look Bad - Banned on Facebook and Shadowbanned on Twitter
Apple, Twitter, Google, Instagram collude to defeat Trump
Twitter’s double standard is even allowing these hash tags to exist, much less the incitement to violence that often accompanies them while banning conservatives.
#polarbearhunting and #KnockOutGame, where blacks try to knock out whites with one blow to the head, thousands of black on white attacks per year, while the only case of a white guy doing it to a black got the DoJ involved