When former President Bill Clinton referred to present President Barack Obama at the Democratic National Convention as "cool on the outside," Clinton was underscoring the notion that Obama is, well, cool.
Since Obama was elected, much has been made of his coolitude. He listens to an iPod. He slow jams the news with late-night comic Jimmy Fallon. He wears shades, drinks beer, taps into social media and sings Al Green now and then. The New Yorker referred to Obama as Mr. Cool.
Which got us to thinking — and asking historians — who are the seven coolest presidents in American history?