Kennedy, Ryan P., David Lazer, and Oren Tsur. 2016. “What He Talked About: From Sports to Threats to Foreign Countries, Here Are Seven Years of Obama’s Preoccupations in the Speeches He Gave—charted”. Politico, 2016.
See also:
21st Century Democracy

Abstract
Barack Obama can spin a good phrase, and while his political opponents like to say his actions don’t always match his soaring rhetoric, there’s no denying the man has said a lot: So far in his presidency, he’s given more than 2,000 official speeches, uttering about 3.5 million different words. So what has he actually been telling us? To answer this question in a whole new way, we analysed all of Obama’s speeches through the end of September and looked at how frequently different terms came up. Surprises abound: Afghanistan was the most-mentioned country after the United States. He talks football more than basketball, Pelosi more than Reid and "change" more than "hope" - except in 2012. Here’s a unique look at what’s really on Obama’s mind.