Donald Trump said that http://prntscr.com/duslay
Obama replied: At least I will go down as a president.
I know what he meant by that, but I don't get what's the context hidden between the lines, I don't get the roast, why did people find it so funny? Don't all presidents go down anyway? (be recorded or remembered in a particular way.)
Does he mean Donald Trump wont be remembered? or something?