This approach is evident in his shifting statements about the payment that Michael D. Cohen, his former lawyer, made to a pornographic film actress to keep her from speaking about their alleged affair. In April, Mr. Trump falsely denied knowing about the payment.

After the F.B.I. raided Mr. Cohen’s office, Mr. Trump acknowledged on Twitter in May that Mr. Cohen received reimbursement for the payment and asserted that it had nothing to do with his presidential campaign. Mr. Cohen would later tell prosecutors that he acted at Mr. Trump’s direction and to influence the election.

After the release of an audio recording of the two men discussing a hush-money payment to another woman, Mr. Trump claimed in an August interview on “Fox & Friends” that he did not know about the payments until “later on” and that Mr. Cohen “made the deals.” He then misleadingly compared Mr. Cohen’s actions — a willful violation of campaign finance law — to a civil infraction incurred by former President Barack Obama’s 2008 campaign.

By December, Mr. Trump’s defense had shifted further: “I never directed Michael Cohen to break the law.”

Misleading Vagueness and Fanciful Details

The president is known for being unscripted and loose with language, but he sometimes shows tactical restraint.

After Justice Brett M. Kavanaugh was confirmed to the Supreme Court and in the days before the midterm elections, Mr. Trump told rallygoers in Missouri that “the accuser admitted she never met him, she never saw him, he never touched her, talked to her, he had nothing to do with her, she made up the story, it was false accusations.”

The omission of a name and the use of the words “the accuser” may give the misleading impression that Christine Blasey Ford, who testified to Congress that Justice Kavanaugh had sexually assaulted her when they were teenagers, had recanted her account. But in fact, Mr. Trump was referring to another little-known accuser named Judy Munro-Leighton, who recanted her claim of sexual assault.