Less than 12 hours later, he was free-form again, Trump being Trump, resurrecting a conspiracy theory linking the father of his chief rival from the primaries to John F. Kennedy's assassination. Trump's plunge into a lengthy litigation of past spats with Ted Cruz — even bringing up his retweet of an unflattering photo of Cruz's wife, Heidi — did nothing to assuage Republican fears about their standard bearer after a national convention complicated by unforced errors. Presidential candidates typically come out of their conventions looking ahead to the general election and intent on expanding their appeal beyond the partisans who showed up. Trump took a bizarre look backward at what was billed as a post-convention thank you reception Friday for supporters and staff at his Cleveland hotel. Reviewing one of the ugliest chapters of the nomination contest, Trump mentioned Cruz's father, saying "All I did was point out the fact that on the cover of the National Enquirer there was a picture of him and crazy Lee Harvey Oswald having breakfast." Former House Speaker Newt Gingrich, a Trump supporter who was on the short list for running mate, said: Trump tends to take, very personally, attacks and he tends to counterattack very aggressively. Former NFL quarterback Tim Tebow was billed on the convention speaking program released by the campaign last week, but described his appearance as a rumor and didn't come. [...] on Wednesday, the campaign released a statement blaming a writer for unknowingly lifting passages from the speech.