“Poetic license” is the freedom allowed to writers for achieving literary effects by deviating from facts, conventional logic, or standard grammar and spelling.
“Political license” is the freedom allowed to politicians to make statements deviating from facts, logic, principle, or consistency to achieve electoral effects. Although sanctioned for politicians by long practice, this freedom is denied to ordinary mortals. When they say something silly, they expose themselves to immediate contradiction, derision or rude guffaws.
This gem comes not from Mark Twain nor H.L. Mencken, albeit worthy of their pen. It from a man named John Frary in the comment box here: http://pjmedia.com/rogerkimball/2012/11/20/the-surrealistic-states-of-america/