Reuters did some research with voters who had been backing Robert F. Kennedy, Jr., and finds that Kennedy’s endorsement of Donald Trump is winning votes for Trump. Although the Reuters research was small, the article also summarizes other evidence to support the same conclusion. See it here.
Kennedy only became an ally of Trump after enduring months of attacks on his ballot access by Democratic Party officials and sympathizers.
The article notes that some voters who previously voted Democratic have become unhappy with the Democratic Party for its efforts to block ballot access for various candidates.