That’s the most likely possibility.

There is no "most likely possibility" at this point. We don't know anything.

It might have something to do specifically with Donald Trump. It might not. It might be a situation like the Reagan or Ford assassination attempts - the assassins had no opinion about the officeholder personally or politically, they just wanted/felt compelled to attack the head of government for some ulterior motive. It might be a Leon Czogolz scenario, where the attack was motivated by a rejection of the nature of government or politics, not the candidate (ie. the assassin would have killed any President or candidate, Republican or Democrat). It might be a situation where he shot at the candidate because the voices in his head told him to, or because he wanted to "live forever" by doing something that would be in the history books, or commit suicide by counter-sniper, or some other crazy reason.

It still very well might be something specific to the politics of Donald Trump - but a non-trivial number of U.S. assassinations actually had very little to do with the politics of the person person being targeted, and we should always consider that possibility.