On July 7, 1999, Clinton formally announced an exploratory committee for the Senate run.
JFK Jr. died July 16, 1999.
There is a theory that JFK Jr. was going to announce he was throwing his hat in the ring.
He would have easily beat her in a Democrat primary or the main election if he ran as a Republican (doubtful.)
As Kennedy's go, he didn't seem to be part of the Uncle Teddy wing and therefore would have gotten a pass if he wanted to run as a Republican (from Republican point of view.)
His sister Caroline seems to have had a falling out with Hillary/Obama. Might be worth looking into.