A thought on politicians shouting Niebuhr

I'm about a third of the way through The Irony of American History, and one thing I don't understand is how any national politician could ever cite Niebuhr as any sort of influence. That is too categorical. What I'm trying to say is this book seems to be a call for a national humility, a broad caution against a kind of state-sponsored rationalist utopianism, as well as caution against the sort of "American Exceptionalism" that's basically taken as a given for anyone running for president. Am I reading this wrong? It seems to be president you have to not simply be proud of your country, but believe that it virtually on a mission from God. Is Niebuhr just another MLK? Some guy people shout-out because it sounds good, meanwhile ignoring the persons more politically unpopular opinions? Again, I'm only a third of the way through. I could have this wrong.