“I was taken aback by the amount of space in President Obama’s speeches that are devoted to a full frontal assault on Donald J. Trump and his administration,” said Karl Rove, the political strategist for former President George W. Bush. “He spends a considerable amount of his time to get up there and trash Trump.”
Ron Kaufman, who was White House political director for the first President George Bush, said Mr. Obama’s language had been strikingly harsh from one president about another. “If you go back and dig up some of the pretty nasty things President Obama has said, I think you would be a bit surprised,” he said. “He gets away with it because of his style.”
Not since Theodore Roosevelt and Herbert Hoover has a president hit the campaign trail after leaving office to actively take on his successor in quite the way Mr. Obama has. Roosevelt actually mounted a comeback against his handpicked replacement, William Howard Taft, while Hoover castigated Franklin D. Roosevelt’s New Deal program as “despotism” at the Republican convention in 1936.
Other former presidents have been critical of their successors, too. Jimmy Carter became a vocal opponent of George W. Bush’s invasion of Iraq, calling his administration the “worst in history.” But with Mr. Carter and others, these were one-off comments in interviews or other public settings, not a systematic indictment on the campaign trail.
Until this cycle, Bill Clinton has been a regular campaigner for fellow Democrats, not least his wife, but even as he assailed Republican ideas, he generally refrained from directly attacking his successors. As in previous years, the younger Mr. Bush has been out on the trail this fall, but has largely kept his post-White House campaigning to closed-door fund-raisers and studiously avoided criticizing either Mr. Obama or Mr. Trump.
Mr. Obama’s criticism of Mr. Trump reflects a deep antipathy he feels for his successor, whom he called a “con man” and a “know nothing” during the 2016 campaign. Mr. Trump was the leading promoter of the lie that Mr. Obama was not born in the United States, a conspiracy theory that irritated the 44th president.
Mr. Obama has never been effective at translating his own popularity to other Democrats — the party lost all three elections while he was president when his name was not on the ballot — but he seems liberated as he finally unloads on Mr. Trump. “He wants to be in the game and he’s really energized doing it,” said Bill Burton, a former aide who caught up with Mr. Obama at a campaign stop in California.