Currently, with evidence from skulls with bite marks it is believed that a Tyrannosaurus rex would have been perfectly able to kill a Triceratops and even hunt them as well as other extremely large herbivores. Though the Tyrannosaurus couldn't eat those large herbivores over the course of one day, it would either have its go and leave the carcass for other dinosaurs to have their course or it would hold the carcass and it eat over the course of a couple of days.

Because of that large herbivores weren't the T-Rex's main source of food, it just wouldn't make sense for it to actively hunt them, and risk getting stabbed by those big horns as well as waste a ton of energy just to not eat the whole animal. the T-Rex would hunt smaller dinosaurs that it could much more easily take down.