I just recommended the book. Not volunteering as your research assistant. Caro is the foremost historian on LBJ. All you have to do is Google him if you want to know his credentials. If you are interested in the topic, read his book. If not, don't. I've explained his arguments as best I can remember. LBJ was increasingly unpopular in the south because of his evolving stance on Civil Rights. As a local politician running for office in Texas in his earlier career, LBJ was never a civil rights advocate. Once his aspirations became the presidency, he realized that he could not be viewed as a southern segregationist and win national office. So he alienated many of his previous supporters in places like Texas by strongly supporting Civil Rights. As a result, it's not clear that dropping LBJ from the ticket would have hurt JFK in Texas. In fact, it might have helped him in the South depending on who he decided to replace him with. Perhaps another more popular Southerner. I don't think any decision had been made on dropping LBJ by Nov. 22. So your question contains a false premise as to why JFK would campaign in Texas while planning on dropping LBJ. He had not made any decision at that point.
btw: Caro who has reviewed more documents and interviewed more people associated with LBJ than anyone else indicated he came across no evidence of his involvement in the JFK assassination. And Caro has leveled some fairy damning criticisms of LBJ. So it is not a case of subject envy.
Well stated. Although it's not clear to me that LBJ's support for civil rights was hurting him that much in Texas. He did receive 63% of the Texas vote when he ran for reelection in 1964. Unlike the other Southern states Texas at that time didn't have Jim Crow segregation (remember several black citizens of Ft. Worth attended the breakfast that morning; and the TSBD didn't have segregated bathrooms or lunch rooms). So any civil rights bill wouldn't have affected the state too much; certainly not as much as those states practicing segregation.
Just to add: LBJ received 55% of the vote for the Senate in 1954. Six years later he ran for the Senate again (yes, while also on the ticket with JFK) and received 58% of the vote. So his pro-civil rights views seemingly didn't hurt too much.
It's interesting to note that four days after the assassination that LBJ called Rev./Dr. King up asking for his support on the civil rights bill. He told King that the legislation was still stuck in the House (in a sub-committee!) and that Congress was going to adjourn without passing it.
Dallek suggests that the Kennedys were waiting for the Baker investigation to conclude before making any decision. He says they were leaking stories about possibly dropping LBJ. That is, covering themselves.