Yes, because if Nikki had beaten Trump then the DNC would simply have ordered their voters to vote for Biden; and they would have done so. She could not have split the Dem Party ticket. RFK, Jr. however is definitely GOING to split the Dem Party ticket of he r4eally does run as an independent; and thus guarantee Trump's re-election.
It's almost a given that there will at least be an attempt on his life at some point . . . hence no secret service protection. The DNC isn't exactly subtle about this stuff.