I'm not sure whose voices the president was referring to, since schools rarely teach what our nation's founders said, but if they did those OSU students might have recalled the words of Thomas Jefferson:
“Experience hath shown, that even under the best forms of government those entrusted with power have, in time, and by slow operations, perverted it into tyranny.”
And one from Patrick Henry, "guard with jealous attention the public liberty. Suspect everyone who approaches that jewel. Unfortunately, nothing will preserve it but downright force. Whenever you give up that force, you are inevitably ruined."
And of course, there's the famous line from Ronald Reagan, "Freedom is never more than one generation away from extinction."
So, yeah, I guess a few people have suggested that "tyranny is always lurking around the corner."