Donald J. Trump could not hide his anger. Sitting at the front of a crowded New York courtroom this week, he folded his arms tightly across his chest. He tossed his head and scowled. He stared into the middle distance and scrolled through his phone.

His ire was directed at Michael D. Cohen, his former personal lawyer and fixer, who had taken the witness stand 15 feet away and had promptly called Mr. Trump a liar. Mr. Cohen has told his share of lies as well. But in court, he swore he had done so “at the direction of, in concert with and for the benefit of Mr. Trump.”

Mr. Cohen’s two days of dramatic testimony this week provided the first glimpse of what could become a familiar scene: Mr. Trump, sitting at a defense table, watching as a lawyer who once did his bidding now cooperated with the authorities seeking to hold him to account.

On the same day Mr. Cohen began his testimony, Jenna Ellis, who had sought to help Mr. Trump overturn the results of the 2020 election, pleaded guilty to state charges in Georgia. She was preceded by Sidney Powell and Kenneth Chesebro, both lawyers who worked with Mr. Trump’s campaign, both now expected to cooperate in the criminal case that the Georgia prosecutors brought against him.

The circumstances surrounding the Georgia criminal case and the Manhattan civil fraud trial are vastly different. But near the center of each case are lawyers who pledged public fealty to Mr. Trump — until they very publicly did not.

Mr. Trump has long relied on a phalanx of legal attack dogs to speak on his behalf, or to do or say things he would rather not do or say himself. And because Mr. Trump has such a tenuous relationship with the truth, those lieutenants often spread a message that prosecutors and investigators consider to be outright lies. Lies about an election he lost, a relationship with a porn star he may have had and a net worth he may not quite have achieved.