Public criticism from an ex-president is certainly rare, particularly in the last few decades, but there are many examples of it, even of personal attacks. Here are a few examples:
In fact, former presidents have been downright insulting at times. “President Theodore Roosevelt called his successor President William Howard Taft a fathead, a puzzle-wit with the brain of a guinea pig,” Goodwin said.
“President Herbert Hoover claimed the despotism of President Franklin Roosevelt was poisoning America. Hoover worked for the last 20 years of his life on a massive indictment of FDR’s handling of World War II. He was so obsessive about this that his heirs decided not to have it published and put it into storage,”
In more recent times, Jimmy Carter “criticized President Bill Clinton’s morals after the Monica Lewinsky scandal and criticized President Ronald Reagan for a perceived failure to accept his responsibilities as president,” Goodwin said.
Carter also called George W. Bush’s administration the “worst in history” in terms of “adverse impact on the nation around the world.”
George H.W. Bush
“He has the nerve to blame Republicans for his own failures and the shortcomings of the Democratic Congress,” — Pittsburgh Post-Gazette
“I have tried to stay out of all the Washington mess,” Bush said Saturday at the end of a keynote address to the Safari Club International’s 27th annual hunters’ convention. “But I must confess I have been deeply concerned by what appears to be a lack of respect for the office I was so very proud to hold.” — The Associated Press
Former President Jimmy Carter, responding to criticism from President Reagan, said tonight that while his Administration made mistakes, “we did not spend four years blaming our mistakes on our predecessors” …
“My offer still stands,” Mr. Carter said at a Democratic National Committee fund-raising dinner. “When he is ready to accept those responsibilities, I’ll be there to help him.” — The New York Times
‘There is always the temptation for an incumbent politician to blame all his mistakes on his predecessor. Most are willing to withstand the temptation. Mr. Reagan, apparently, is not,’ Carter said. ...
But to try to forego blame and say all these problems are my predecessor’s fault is patently irresponsible and ill-advised,” — United Press International
“The Carter economic policies have been a catastrophe. They’ve been disasters. We handed them the economy on a silver platter,” Ford said, arguing that the rate of inflation was less than 5 percent when he left office and that unemployment was going down. “The president blew it.” — The Associated Press
Dwight D. Eisenhower
After Kennedy’s victory in the election, he reportedly stated with sarcasm, "We have a new genius in our midst who is incapable of making any mistakes and therefore deserving of no criticism whatsoever” Eisenhower the President quoted on the Eisenhower National Historic Site website