The assassination luckily failed thanks to the intervention of the Danvers sisters, but it directly resulted in the origin of Metallo.
Lex has already done major damage to the good guys of National City, and we haven’t even seen him in the flesh.
Supergirl hasn’t gone in-depth on Lena’s childhood interactions with Lex, so we don’t know at this point if the madness that drove him to declare war on Superman started early.
Earlier this season, he contracted an assassin to go after his sister because she dared to rename the family company in the wake of his incarceration.