"We are just waiting for the people to see the light," Sen. Antonio Trillanes IV told the Financial Times. "Once they do, and I certainly hope they do, things will change."
Trillanes has "launched a campaign" to impeach Duterte, FT reports, for the president's complicity in murder, as well as in graft.
Another senator is going further, calling Duterte a "sociopathic serial killer" and "psychotic murderer," and comparing him to The Joker character in the Batman series.
"Now the time has come again for us to be brave and stand up to another criminal dictator and his evil regime," said Sen. Leila de Lima, a former justice secretary. She wants Duterte's cabinet to rule the president "mentally incapacitated" and have him replaced.
A spokesman for Duterte recognized the senator's "colorful language," but remarked that the president allowed public demonstrations against him, proving he is no despot.
De Lima is currently facing arrest on drug charges, Sky News reports. Trillanes previously served seven years in prison under a previous president for alleged participation in a military uprising.
FT reports that more than 7,000 have been killed in the national drug war launched since Duterte entered office last June. Duterte previously was the mayor of Davao City, where he is widely reported to have backed death squads in a manner that is now being seen nationally.