Weiss' contemporaries noted his objection's to Long's politics, which he apparently was so wrought over that they brought him to tears. He viewed Long as a tyrant, and once claimed that he would kill him (Long inspired extreme rhetoric from all sides, and such threats were not uncommon).

That said, there isn't proof that it was an overly premeditated act. Weiss didn't leave behind a note or manifesto, spent the day of the assassination in relatively high spirits, and in fact told his wife he was going out on a house call the night of the assassination. Weiss kept a pistol in his car as a gun collector, and might've acted impulsively, since Long was in Baton Rouge irregularly as senator. An in-law believed that Weiss' broodings had made him mentally unstable to the point where he made a spur of the moment decision to become a "martyr to liberty".

Some dubiously sourced accounts tie Weiss to a larger conspiracy targeting Long due to his opposition to white supremacy, but lack definitive proof.

Source: T. Harry William's Huey Long