The relationship between classical rhetoric and contemporary political oratory is complex.  The ethos associated specifically with presidential oratory represents a negotiation between multiple personae and audiences.  As the chief executive of the United States, the president must claim the "I" position as a speaker of individual action and yet he must also represent America as a collective of citizens and testify from the perspective of the common "we." 
 
Today, our nation saw evil, the very worst of human nature. And we responded with the best of America -- with the daring of our rescue workers, with the caring for strangers and neighbors who came to give blood and help in any way they could.  Immediately following the first attack, I implemented our government's emergency response plans. Our military is powerful, and it's prepared. Our emergency teams are working in New York City and Washington, D.C. to help with local rescue efforts. (George W. Bush 9-11-01)

Presidential rhetoric must also draw on the natural speech idiom, but it must do so in a form that demands the use of elevated speech, what speech writers call "laying marble."   Although Bush has cultivated a homespun Texas image, in the speech about September 11 before Congress he employs a topos straight out of ancient rhetoric of the classical period and raises the shield of the fallen hero and remembers him to the crowd by name.
 
And I will carry this:  It is the police shield of a man named George Howard, who died at the World Trade Center trying to save others.  It was given to me by his mom, Arlene, as a proud memorial to her son.  This is my reminder of lives that ended, and a task that does not end. (George W. Bush 9-20-01)