Mr Sanders warned that the war would further deepen instability in the world.
Mr Khamenei was killed in his office after it was hit by missiles on Saturday.
She accused Mr Trump of reneging on his campaign promise to end foreign wars.
Mr Khamenei was killed Saturday after the U.S. and Israel launched a pre-dawn assault on the country.
The strikes by the U.S. and Israel have seen Iran’s Supreme Leader Ayatollah Ali Khamenei and top members of his regime dead.
Images posted by the White House, Mr Trump and a team of officials closely monitoring the military action tagged “Operation Epic Fury.”
“The world is a better place without them,” the IDF said.
Israeli Prime Minister Benjamin Netanyahu had said there were many signs Mr Khamenei had been killed in the strikes targeted against his residence.
The U.S. and Israel launched a joint attack on Iran early Saturday, claiming it was meant to remove “threats” posed by the Iranian “regime.”
The death of Mr Khamenei, 86, ends his reign of over three decades over Iran.
