It was World Class Championship Wrestling all over again, except with Donald J. Trump swaggering onstage instead of a Von Erich brother, and New Jersey Gov. Chris Christie turning good guy to tag-team against whatever mortal enemies might lie in wait.

The crowd’s hero strode in to cheers and loud rock music, belittled an unseen opponent as a “little frightened puppy” and a “choke artist,” and then taunted critics that he would “sue you like you have never been sued before.”

Bill Mercer, the retired local TV anchor and 1980s host of World Class’ syndicated wrestling telecasts, recognizes it all.

“Good night, yes, it’s just like wrestling — the hype, the yelling, the threats and calling people names,” Mercer, 90, said by phone from North Carolina...