To expand on what some other people have said, African American votes were very intensely suppressed. Only 6 or 7 % of Mississippi blacks were registered to vote in 1961, and in some heavily black counties there weren't any registered African Americans. The people in power held a lot of control over who they would let register to vote. In many urban counties for instance, they would let honored or token blacks like lawyers, doctors, veterans and the like to register, but not anyone else, and certainly not enough to influence the election outcome. Also, of those who were registered to vote, even fewer would dare turn out to vote. Of all the Southern States, Mississippi was the worst in this regard. Most of those votes for Johnson probably came from white's who either weren't put off by his opposition to segregation, or understood that segregation was wrong and wanted to see it ended.
Actually, as Kevin Phillips shows on page 264 of
The Emerging Republican Majority, most of the 52,618 votes for Johnson came from poor hills whites who were racially as conservative as the Goldwater voters, but who could not accept the thought of privatization of Social Security or of the Tennessee Valley Authority. The same was true of the 19,384 votes for Truman in 1948. In the northeastern bloc of Tishomingo, Prentiss, Alcorn and Itawamba Counties – which are over 90 percent white – both Truman and LBJ obtained over 30 percent of the vote.
Almost every one of these residual Democratic voters shifted to Wallace in 1968. If you look at those four counties noted in the previous paragraph, they gave Wallace between 5 and 20 percent
more of their votes than they had given Goldwater in 1964 or Thurmond in 1948. If the Voting Rights Act had not been passed to enfranchise blacks, Humphrey in 1968 and McGovern in 1972 would have probably gained no more than
4 or 5 percent of the total Mississippi vote (vis-à-vis 23 percent and 19 percent as it was).
Even with Mississippi being the worst offender in this regard, 87% for Goldwater is still pretty extreme. It's also important to consider that the way Johnson handled the Mississippi Freedom Democratic Party Delegation at the convention did him no favors. For those who don't know, two delegations from Mississippi showed up at the 1964 convention, the Democratic Party of Mississippi's delegation, who was selected by an all white primary, and the Mississippi Freedom Democratic Party delegation, comprised of black and white activists seeking to claim that that the Mississippi Democratic Party was illegitimate. Johnson was upset by the MFDP's presence, but he tried to be diplomatic by letting them have a few seats. The Mississippi Democratic Party delegation walked out unhappy, and the MFDP felt like they got the short end of the stick. This probably had an affect on Mississippi being much more Republican than Alabama where Johnson wasn't even allowed on the ballot.
That’s an interesting thought. It is true though that the issue of TVA privatization was not so important even in Tishomingo, Prentiss, Alcorn or Itawamba as it was in those five North Alabama counties which Goldwater actually lost to an unpledged slate sponsored by George Wallace. Comparing Mississippi with
North Louisiana – where fewer blacks were registered than in Alabama but where Johnson was on the ballot due to support from racially moderate French South Louisiana parishes – we see that Goldwater did not obtain over 90 percent in any parish. Thus, it is possible that the mainstays of the white Mississippi Democratic Party in the Black Belt did feel anguished to a greater extent than in North Louisiana. However, figures from the North Louisiana Black Belt parishes of Madison and Tensas suggest this influence could only have cost LBJ a few percent of the vote. He probably could have done no better in Mississippi than 20 percent with black registration what it was.
