Judge Jackson said she was particularly disturbed that some of the contacts occurred after Mr. Manafort had been specifically ordered by another federal judge to avoid all contacts with witnesses involved in Mr. Mueller’s investigation or the prosecution of him. That judge is overseeing a separate case in Northern Virginia, where Mr. Manafort faces additional charges of tax evasion, bank fraud and failure to report foreign bank accounts.

“I have no appetite for this,” Judge Jackson told Mr. Manafort shortly before he was led out of the courtroom to be transported to jail. “I have struggled with this decision.”

But she said that even if she explicitly ordered Mr. Manafort never to contact any of the government’s 56 witnesses, she could not be certain he would comply. “Will he call the 57th?” she asked.

She noted that she had previously warned Mr. Manafort about his conduct while on house arrest after prosecutors complained that he had broken the rules against contacts with the news media.

“I’m concerned you seem to treat these proceedings as another marketing exercise,” she said. She implied that she was running out of patience with him, saying the case “continues to be to this minute extraordinary.”

Mr. Manafort’s lawyers suggested that he had reached out innocently to his former colleagues, not knowing whether they had been contacted by Mr. Mueller’s team. But Mr. Andres said Mr. Manafort was simply deceiving the court, just as he had deceived law enforcement agencies and tax authorities over the years.

“It’s inconceivable that he did not know they were potential witnesses,” he said.

Mr. Trump has sought to distance himself from Mr. Manafort, who worked for his campaign for nearly five months, including three months as campaign chairman, before he was ousted in August 2016 amid controversy over his Ukraine work. “Mr. Manafort worked for me for a very short period of time,” the president said on Friday morning.

“He worked for me, what, for 49 days or something?” he added. “I feel badly for some people because they have gone back 12 years to find things” — an apparent reference to the allegations against Mr. Manafort.

Asked if he was considering pardons, Mr. Trump said: “I don’t want to talk about that. No, I don’t want to talk about that. But look, I do want to see people treated fairly.”

Besides violating laws that require the disclosure of lobbying on behalf of foreign interests, the government alleges, Mr. Manafort laundered more than $30 million in income he received over nine years of lobbying for Mr. Yanukovych and his political parties or allies.

As evidence that Mr. Manafort lobbied in the United States, prosecutors submitted a four-page memo that Mr. Manafort wrote to Mr. Yanukovych detailing his campaign to convince members of Congress, the State Department and the Western news media that Mr. Yanukovych was a champion of democratic reforms.

The government claims that the offenses are part of a complex financial conspiracy led by Mr. Manafort and aided by Rick Gates, Mr. Trump’s deputy campaign chairman, and Mr. Manafort’s right-hand man, Mr. Kilimnik, who has been linked to Russian intelligence.

Mr. Manafort’s first trial, in Northern Virginia, is scheduled for next month.