You can't compare a man abandoning the democrats in 1952 or before, with a man becoming a democrat in the radically leftist democrat party of the post 1960s, a lot of great Americans USED to be democrats, but not since the left totally took over the party in the 1960s.
It is a point of mystification to lots of old "lunch-bucket" Democrats ("hard hats" in 1968, when they voted for George Wallace, and "Reagan Democrats" when they went for the Gipper in the 80's) that the Democratic Party has been taken over by hard-line groups of one enthusiasm or another, whose common ground is that they are all fundamentally neo-Stalinist.
That change was effected by the Alinskyite takeover of the Democratic Party after 1968.
And they never reflect why it was that the old liberal Democrats' narrow loss to Nixon in 1968 somehow "delegitimized" the traditional Democrats, while -- somehow -- the Alinskyites' and their neo-Stalinist candidate's rejection in a 49-state landslide in 1972 in favor of that selfsame Richard Nixon despite the uniform support of the MSM, was not.