The true Trump believers won’t changes. It’s his soft support that would look at RFKjr. They like his Covid/vax stances and his anti Ukraine financial support . And some of the greenie weenie crowd was open to Trump for some of his other stands that Bobby Jr fulfills. I don’t think it’s huge leakage, but in key swing states it could make a difference. For better or worse look what Nader did to Gore in Florida.
Pat Buchanan also took votes from Bush in 2000.