Joe Scarborough, the former Republican congressman and influential host of the eponymous MSNBC program Morning Joe, has been so hostile in public and private toward the Florida senator that it’s now turning heads in Republican circles.

On television and social media, Scarborough has dismissed Rubio as a wannabe student-council president and lambasted him for lying to the American people. Scarborough’s distaste is returned in kind: Rubio doesn’t think much of him, either…

According to multiple sources in Florida, the friction between the two dates back to Rubio’s Senate race in 2010 against former Florida governor Charlie Crist, when Scarborough argued that Rubio was too young, too unseasoned, and — perhaps most seriously — too compromised by ethical issues to win the Senate seat. In picking up this line of criticism, Scarborough has once again become one of the senator’s chief antagonists, this time in his quest for the White House…

Others say that Scarborough is turned off by Rubio’s slickness. “Everybody who knows Rubio doesn’t support Rubio,” says John Morgan, a Florida trial lawyer for whose firm Scarborough once worked, because “Rubio will tell you anything you want to hear.” And Scarborough, he says, is wondering, “‘How has he been able to pull off this con?’ He’s frustrated that people are believing it.”