Vietnam and Cuba in particular (along with making some of the wrong enemies in gov’t) - both had big policy shifts once LBJ took over. Now, did the masterminds of the plot just assume LBJ would be more to their liking in terms of policy? Maybe.

But

1) killing the president is a big fucking deal - the biggest fucking deal - and I dont know how you can “pull the trigger” unless you’re 100% sure on policy changes.

2) The magic bullet theory is pretty much toast … clearly there was some sort of conspiracy and multiple shooters. That much is obvious. The fact that so much of the investigation remains classified begs the question what the powers that be believe the public truly can’t handle seeing 60 years later. A CIA-adjacent - but unofficial - conspiracy doesn’t quite rate that high for me. A VP being actually involved? Yeah … that could do it.