It may not be fair and there may be different standards, but let it be a lesson. Anyone who threatens a president is an idiot and should expect to be prosecuted and perhaps thrown in jail. We don’t know enough to know if he was jailed simply for writing a poem. This is a lesson in “being stupid can get you in trouble”.
BUT SPENCER DIDN’T THREATEN OBAMA!!!
THE POEM WAS PUBLISHED IN 2007!!!
When any innocent man goes to prison in the USA, all Americans go to prison.
Unless it's a Republican president, apparently. If it's a Republican president, one may write books, write screenplays, make movies, and do stand-up comic routines about it and be the toast of academia and Hollywood.
But you are right. Threatening the life of a president—regardless of political affiliation—is seriously wrong and should be vigorously prosecuted.