The term “American exceptionalism” has an effect in American political rhetoric similar to the effect that a fog machine has on a crowded dance floor. It obscures and makes easier things that would be more difficult without its presence.
Some people use “exceptionalism” to describe allegiance to the principles espoused in the U.S. Constitution. I agree that in the age of Tocqueville, American exceptionalism described America’s distinctions from (particularly continental) Europe. The establishment of a new country provided an opportunity to do things differently.
However, an assemblage of phenomena like Congress’s half-century shrug and sigh at imperial presidentialism and visuals like this call into question the extent to which the republican constitutional vision of the nation’s founders and the institutions it spawned actually constrain American politics today.