It’s theoretically possible for an organized effort to use a primary (open or closed) to choose a different nominee; many Republicans tried that in several states to vote for Hillary in 2008. Nonetheless, Obama still won. It could happen, but, IMO, it’s very unlikely.
Limbaugh and others had no idea how despised the Hildabeast had become.
Easy when it's an open primary of course - anyone can vote - could be done in a much looser effort. Harder in a closed state - some states control how often you can switch parties. Much more difficult to coordinate a massive party switch in a closed state. Obviously much easier to control a party-switching problem in a closed state.
Open primaries make no sense to me and as far as I'm concerned it is a fiasco for the party holding the primary.