What if Oswald had managed to kill Johnson while in the motorcade in Dallas along with Kennedy? It would not be anything really difficult, of course. LBJ was a few cars behind Kennedy and as clear a shot seemed to be there if Oswald simply waited. So what would this affect? Who succeeds these men to the white house? And how do Civil Rights and Vietnam go under the succeeding leader, etc.?
(I don't put WI at the front of this because I may do a TL at some point with this, or someone else can hijack the thread to do a TL if interested)