Trump is the only one to threaten to go third party. Gary Johnson is running on the libertarian ticket. Paul has no interest. Again, the voters of KY., would ignore Levin. So what is Levin going to threaten Trump with? Nothing, he’s powerless.
When did Ron Paul say he has ruled it out? When has he categorically denied he would ever do it? Right now there are enough people stroking his ego and eccentricity to get him to do just about anything.
As for Trump, he has always been Obama’s card to play. Trump is a tool.
Your right Levin is powerless, but for what it’s worth he use his mic to oppose the Pauls if pappy goes rogue.