Modern political discourse is a carefully elaborated type of discourse containing numerous language forms, whose purpose is not only to transfer information, but also occasionally to change listeners' attitudes and opinions. Euphemisms have always been an inseparable part of political discourse, and this paper attempts to explain cognitive mechanisms underlying the occurrence of euphemisms in speeches on war by two presidents of the USA, the former president George W. Bush and the current president Barack Obama. In the majority of the available resources on euphemism, metaphor and metonymy are listed as devices of euphemism formation, and since these two cognitive and conceptual phenomena have now for decades been regarded as integrated parts of human thought, they are in charge of the formation of the majority of the mentioned euphemisms that have been extracted from the speeches of the two presidents, and divided into groups according to the topic of euphemisation and cognitive mechanisms underlying their occurrence – conceptual metonymy and metaphor. There is little available literature that links the language phenomenon of euphemisms with cognitive linguistics, and that is precisely the purpose of this paper: to illuminate the purpose and aim of the use of euphemisms in the speeches of the two presidents via cognitive mechanisms in charge of their occurrence, as well as their effects on listeners’ attitudes and opinions, with the help of Fillmore's semantic frame theory, as well as its later adaptation to the American political discourse by George Lakoff. The topics that both presidents consider either taboo, unpleasant, inappropriately presented, or they see them as threats to their face are: war, army and soldiers, and death. Conceptual metonymy is the cognitive mechanism that is prevailing for these three most commonly euphemised topics in the speeches of both presidents, and it is followed by conceptual metaphor.