During the '76 campaign, Ronald Reagan had suggested that President Ford forgot to wear his helmet when he played football for Michigan. He said it with a twinkle and a winning smile, but he said it. Lyndon Johnson was the one who said that, apparently back in the 1960s. Source:
https://www.nytimes.com/1974/09/15/archives/under-fords-helmet-a-congressional-mind-brought-to-bear-on-the.html. [Sorry, I hate to quote the NY Times, but there it is....]
Reagan certainly came across so well that he
could have said it without seeming mean-spirited. However, I'd be very surprised if he repeated one of Lyndon Johnson's barbs.
Regardless, the internal backbiting now makes conservatives look petty and won't serve us well in the long run. We should stick together.