I heard that the song High Hopes was written for Kennedy, is this true? And if it is why hasn't an artist write an original song for their Candidate since? Istead of said Canid ripping off a song?

That song is from the movie A Hole In The Head. Frank sang a modified version as a political song, but that was a different song sang in the same tune. The actual song was a big hit at the time. Singers changing lyrics to support candidates is still a thing.

I'm embarrassed to be an American

Where I get charged fees

And I won't forget the man who won't die that did this crime to me

There I did a bad parody about a piece of shit, it's almost as cringe as the original.